allow client to pass null if there are no uniforms

Relies on https://skia-review.googlesource.com/c/skia/+/271738

Change-Id: I990ed71c847af472252b6efc3abde83fc741abfa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/271698
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
2 files changed