assert that non-empty clips have non-empty bounds

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2084603002

TBR=

Review-Url: https://codereview.chromium.org/2084603002
diff --git a/src/core/SkAAClip.cpp b/src/core/SkAAClip.cpp
index f71d7b6..088ee55 100644
--- a/src/core/SkAAClip.cpp
+++ b/src/core/SkAAClip.cpp
@@ -191,6 +191,7 @@
         SkASSERT(fBounds.isEmpty());
         return;
     }
+    SkASSERT(!fBounds.isEmpty());
 
     const RunHead* head = fRunHead;
     SkASSERT(head->fRefCnt > 0);