Simplify the frame testing logic in callers to grab borders

A lot of code did something similar to:

  MetaFrameBorders borders;

  if (window->frame)
    meta_frame_calc_borders (window->frame, &borders);
  else
    meta_frame_borders_clear (&borders);

Sometimes, the else part was omitted and we were unknowingly using
uninitalized values for OR windows. Clean this up by just testing
for a NULL frame in meta_frame_calc_borders and clearing for the
caller if so.

https://bugzilla.gnome.org/show_bug.cgi?id=643606

src/compositor/meta-window-actor.c

@@ -1616,24 +1616,16 @@ meta_window_actor_update_bounding_region_and_borders (MetaWindowActor *self,
                                                       int              height)
 {
   MetaWindowActorPrivate *priv = self->priv;
-  MetaFrame *frame;
   MetaFrameBorders borders;
   cairo_rectangle_int_t bounding_rectangle;
 
-  bounding_rectangle.x = 0;
+  meta_frame_calc_borders (priv->window->frame, &borders);
-  bounding_rectangle.y = 0;
-
-  frame = priv->window->frame;
-  if (frame != NULL)
-    {
-      meta_frame_calc_borders (frame, &borders);
 
   bounding_rectangle.x = borders.invisible.left;
   bounding_rectangle.y = borders.invisible.top;
 
   width -= borders.invisible.left + borders.invisible.right;
   height -= borders.invisible.top + borders.invisible.bottom;
-    }
 
   bounding_rectangle.width = width;
   bounding_rectangle.height = height;
@@ -2163,10 +2155,7 @@ check_needs_reshape (MetaWindowActor *self)
   meta_shaped_texture_set_shape_region (META_SHAPED_TEXTURE (priv->actor), NULL);
   meta_window_actor_clear_shape_region (self);
 
-  if (priv->window->frame)
   meta_frame_calc_borders (priv->window->frame, &borders);
-  else
-    meta_frame_borders_clear (&borders);
 
   region = meta_window_get_frame_bounds (priv->window);
   if (region != NULL)

src/core/constraints.c

@@ -573,7 +573,7 @@ place_window_if_needed(MetaWindow     *window,
                  META_MAXIMIZE_VERTICAL : 0), &info->current);
 
           /* maximization may have changed frame geometry */
-          if (window->frame && !window->fullscreen)
+          if (!window->fullscreen)
             meta_frame_calc_borders (window->frame, info->borders);
 
           if (window->fullscreen_after_placement)

src/core/frame.c

@@ -322,6 +322,11 @@ void
 meta_frame_calc_borders (MetaFrame        *frame,
                          MetaFrameBorders *borders)
 {
+  /* Save on if statements and potential uninitialized values
+   * in callers -- if there's no frame, then zero the borders. */
+  if (frame == NULL)
+    meta_frame_borders_clear (borders);
+  else
     meta_ui_get_frame_borders (frame->window->screen->ui,
                                frame->xwindow,
                                borders);

src/core/window.c

@@ -3704,6 +3704,7 @@ meta_window_can_tile_side_by_side (MetaWindow *window)
 {
   const MetaMonitorInfo *monitor;
   MetaRectangle tile_area;
+  MetaFrameBorders borders;
 
   if (!meta_window_can_tile_maximized (window))
     return FALSE;
@@ -3717,15 +3718,10 @@ meta_window_can_tile_side_by_side (MetaWindow *window)
 
   tile_area.width /= 2;
 
-  if (window->frame)
-    {
-      MetaFrameBorders borders;
-
   meta_frame_calc_borders (window->frame, &borders);
 
   tile_area.width  -= (borders.visible.left + borders.visible.right);
   tile_area.height -= (borders.visible.top + borders.visible.bottom);
-    }
 
   return tile_area.width >= window->size_hints.min_width &&
          tile_area.height >= window->size_hints.min_height;
@@ -4646,7 +4642,6 @@ meta_window_move_resize_internal (MetaWindow          *window,
               is_user_action ? " (user move/resize)" : "",
               old_rect.x, old_rect.y, old_rect.width, old_rect.height);
 
-  if (window->frame)
   meta_frame_calc_borders (window->frame,
                            &borders);
 
@@ -5109,10 +5104,8 @@ meta_window_move_frame (MetaWindow  *window,
 {
   int x = root_x_nw;
   int y = root_y_nw;
-
-  if (window->frame)
-    {
   MetaFrameBorders borders;
+
   meta_frame_calc_borders (window->frame, &borders);
 
   /* root_x_nw and root_y_nw correspond to where the top of
@@ -5122,7 +5115,7 @@ meta_window_move_frame (MetaWindow  *window,
    */
   x += window->frame->child_x - borders.invisible.left;
   y += window->frame->child_y - borders.invisible.top;
-    }
+
   meta_window_move (window, user_op, x, y);
 }
 
@@ -5170,10 +5163,9 @@ meta_window_move_resize_frame (MetaWindow  *window,
                                int          root_y_nw,
                                int          w,
                                int          h)
-{
-  if (window->frame)
 {
   MetaFrameBorders borders;
+
   meta_frame_calc_borders (window->frame, &borders);
   /* offset by the distance between the origin of the window
    * and the origin of the enclosing window decorations ( + border)
@@ -5182,7 +5174,7 @@ meta_window_move_resize_frame (MetaWindow  *window,
   root_y_nw += borders.visible.top;
   w -= borders.visible.left + borders.visible.right;
   h -= borders.visible.top + borders.visible.bottom;
-    }
+
   meta_window_move_resize (window, user_op, root_x_nw, root_y_nw, w, h);
 }
 
@@ -5814,10 +5806,7 @@ meta_window_get_net_wm_desktop (MetaWindow *window)
 static void
 update_net_frame_extents (MetaWindow *window)
 {
-  unsigned long data[4] = { 0, 0, 0, 0 };
+  unsigned long data[4];
-
-  if (window->frame)
-    {
   MetaFrameBorders borders;
 
   meta_frame_calc_borders (window->frame, &borders);
@@ -5829,7 +5818,6 @@ update_net_frame_extents (MetaWindow *window)
   data[2] = borders.visible.top;
   /* Bottom */
   data[3] = borders.visible.bottom;
-    }
 
   meta_topic (META_DEBUG_GEOMETRY,
               "Setting _NET_FRAME_EXTENTS on managed window 0x%lx "