shell-recorder: save cursor's image hot x/y coordinates

Whenever a new cursor image is loaded also save it's hot x/y
coordinates. The drawing code already respects these values, however
they were never set. This change will place the cursor image at the
correct location as seen on screen. shell-screenshot.c served as
reference.

https://bugzilla.gnome.org/show_bug.cgi?id=792860

src/shell-recorder.c

@@ -325,6 +325,9 @@ recorder_fetch_cursor_image (ShellRecorder *recorder)
   if (!texture)
     return;
 
+  meta_cursor_tracker_get_hot (recorder->cursor_tracker,
+                               &recorder->cursor_hot_x, &recorder->cursor_hot_y);
+
   width = cogl_texture_get_width (texture);
   height = cogl_texture_get_height (texture);
   stride = 4 * width;