workspaceThumbnail: fix window tracking bugs

- We should only call workspaceRemoved() for workspaces that are
  are actually being removed.
- When we have multiple monitors, a window on a secondary monitor is
  on all workspaces, so it ends up in all workspaces _allWindows
  lists, so we can't use previous presence in that list to determine
  whether we need to go ahead and add the actor; allWindows is simply
  the list of windows where we are listening  to notify::minimized.

https://bugzilla.gnome.org/show_bug.cgi?id=667652

js/ui/workspaceThumbnail.js

@@ -297,16 +297,18 @@ WorkspaceThumbnail.prototype = {
             return;
         }
 
-        // We might have the window in our list already if it was on all workspaces and
+        if (this._allWindows.indexOf(metaWin) == -1) {
-        // now was moved to this workspace
-        if (this._allWindows.indexOf(metaWin) != -1)
-            return;
-
             let minimizedChangedId = metaWin.connect('notify::minimized',
                                                      Lang.bind(this,
                                                                this._updateMinimized));
             this._allWindows.push(metaWin);
             this._minimizedChangedIds.push(minimizedChangedId);
+        }
+
+        // We might have the window in our list already if it was on all workspaces and
+        // now was moved to this workspace
+        if (this._lookupIndex (metaWin) != -1)
+            return;
 
         if (!this._isMyWindow(win) || !this._isOverviewWindow(win))
             return;
@@ -601,10 +603,10 @@ ThumbnailsBox.prototype = {
             if (thumbnail.state > ThumbnailState.NORMAL)
                 continue;
 
+            if (currentPos >= start && currentPos < start + count) {
                 thumbnail.workspaceRemoved();
-
-            if (currentPos >= start && currentPos < start + count)
                 this._setThumbnailState(thumbnail, ThumbnailState.REMOVING);
+            }
 
             currentPos++;
         }