note that drawAtlas does nothing if atlas is null

Change-Id: I8d2171b1f51a2beccff8a18f9e6324c08e4b864c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/233076
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
Auto-Submit: Mike Reed <reed@google.com>
2 files changed