This partially reverts 2b650fa6, which resizes source image if destination is smaller than its sizing
margins. Resizing the source image may result in the destination image missing some edges because
of StretchBlt() calls. Same StretchBlt() calls also produce similar results on Windows. So it seems
that Windows don't resize the source image and only resize the margins to try to keep the edges
crisp.

Fix scroll bar thumb missing edges when it's too small.
Signed-off-by: Zhiyi Zhang <zzhang@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>