Use careful_memcpy in case one of the args is null

Change-Id: I945c2c76a0134d609e88d6c38051b0bc6a6787e3
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271738
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
2 files changed