Fix invalid assert in GrMesh::setIndexed

When drawing a single point it's valid for the first and last indices
to be equal.

Bug: skia:6728
Change-Id: Ice8cd89b306ed9564cdd9a77c557628662e18abb
Reviewed-on: https://skia-review.googlesource.com/18904
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
1 file changed