fix builder fuzz

src/pathops/SkOpBuilder.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkMatrix.h"
 #include "SkOpEdgeBuilder.h"
 #include "SkPathPriv.h"
@@ skipping 29 matching lines @@
             *path = temp;
         }
         path->setFillType(fillType);
         return true;
     }
     SkChunkAlloc allocator(4096);
     SkOpContourHead contourHead;
     SkOpGlobalState globalState(&contourHead, &allocator  SkDEBUGPARAMS(false)
             SkDEBUGPARAMS(nullptr));
     SkOpEdgeBuilder builder(*path, &contourHead, &globalState);
-    builder.finish();
+    if (builder.unparseable() || !builder.finish()) {
+        return false;
+    }
+    if (!contourHead.count()) {
+        return true;
+    }
     SkASSERT(contourHead.next());
     contourHead.resetReverse();
     bool writePath = false;
     SkOpSpan* topSpan;
     globalState.setPhase(SkOpGlobalState::kFixWinding);
     while ((topSpan = FindSortableTop(&contourHead))) {
         SkOpSegment* topSegment = topSpan->segment();
         SkOpContour* topContour = topSegment->contour();
         SkASSERT(topContour->isCcw() >= 0);
 #if DEBUG_WINDING
@@ skipping 108 matching lines @@
             sum.addPath(fPathRefs[index]);
         }
     }
     reset();
     bool success = Simplify(sum, result);
     if (!success) {
         *result = original;
     }
     return success;
 }