[graphite] Fix SkBitmap creation for ClipAtlas ProxyCache use.

Using detachPixels() also clears the pixmap's info so we need to make
a copy beforehand.

Bug: b/404880920
Change-Id: I010242ef4529ec7c8108259e78172632b1ab9e25
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/971416
Reviewed-by: Thomas Smith <thomsmit@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed