one more empty contour

Add one more empty contour check.

R=kjlubick@google.com
BUG=skia:6073

Change-Id: Ie971875d37388f6bd86a0bdaeaf9230d64aca38d
Reviewed-on: https://skia-review.googlesource.com/6356
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>

src/pathops/SkOpBuilder.cpp

@@ -92,6 +92,9 @@ bool SkOpBuilder::FixWinding(SkPath* path) {
     SkPathWriter woundPath(empty);
     SkOpContour* test = &contourHead;
     do {
+        if (!test->count()) {
+            continue;
+        }
         if (test->reversed()) {
             test->toReversePath(&woundPath);
         } else {