Fix assert on tessellated stroke join type

Change-Id: Ife539625656dd379a6ab5797bcfe5511dfda1e3d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/316477
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
1 file changed