- it aims to fix https://bugzilla.mozilla.org/show_bug.cgi?id=1264608;
- it's only a partial fix for #3351;
- some tiled images have some spurious white lines between the tiles.
When the current transform is applyed the corners of an image can have
some non-integer coordinates leading to some extra transparency added
to handle that. So with this patch the current transform is applied on the
point and on the dimensions in order to have at the end only integer values.
