fix SkRRect fuzzer assert

fuzzer bug triggers an assert in SkRRect::isValid because
on radius is zero and the other, while small, is not.

The radii are normally both set to zero if one is zero
in SkRRect::setRectRadii. However, subsequently scaleRadii
may set one to zero when normalizing the pair.

Move the clamping code out of setRectRadii so it can be
called from scaleRadii as well.

R=reed@google.com
Bug: skia:
Change-Id: Ib9a86da7212567b2f4b83d99a41cf9ba2c30e9b9
Reviewed-on: https://skia-review.googlesource.com/115701
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
2 files changed