Don't add offsets to nullptr in GrGLOpsRenderPass

Change-Id: I54e4069134e66fee0bd85e96b5e9502a3c1fc7d9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/279087
Reviewed-by: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed