Call setNeedsStencil() when clearing stencil

Bug: chromium:1008312
Change-Id: I6e1d160515c6689ac6d62c40e712df287d47f955
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/248723
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
2 files changed