Refs #1700. Fixed: setItemPrototype crash.

Setting the item prototype without first adding the collection view to a view would cause a crash, as would reloadContent.

This fix makes sure the collection view doesn't try to tile itself unless it has a frame.

AppKit/CPCollectionView.j

@@ -492,6 +492,10 @@ var HORIZONTAL_MARGIN = 2;
         oldItemSize         = _itemSize,
         storedFrameSize     = _storedFrameSize;
 
+    // No need to tile if we are not yet placed in the view hierarchy.
+    if (!frameSize)
+        return;
+
     [self _updateMinMaxItemSizeIfNeeded];
 
     [self _computeGridWithSize:frameSize count:AT_REF(count)];