fix mapRect to always return the same as rectStaysRect

Bug: skia:
Change-Id: I7c19703613b3173942a12153b30e9951f35c0008
Reviewed-on: https://skia-review.googlesource.com/61820
Reviewed-by: Cary Clark <caryclark@google.com>
Commit-Queue: Mike Reed <reed@google.com>

src/core/SkMatrix.cpp

@@ -1128,7 +1128,7 @@ bool SkMatrix::mapRect(SkRect* dst, const SkRect& src) const {
         src.toQuad(quad);
         this->mapPoints(quad, quad, 4);
         dst->set(quad, 4);
-        return false;
+        return this->rectStaysRect();   // might still return true if rotated by 90, etc.
     }
 }