[shaper] Do nothing instead of crashing when no CTFont

Bug: b/341104766
Change-Id: I7c4ca5f3c92526f313571ccce6c3d2d5cc527506
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/856030
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
1 file changed