Force snapBackImage() to N32 for image filters

Change-Id: I6232413452488d11782fc6ae2d5927bac2a3a26d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/214363
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
1 file changed