if the winding of the top can't be computed, give up

src/pathops/SkPathOpsOp.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkAddIntersections.h"
 #include "SkOpCoincidence.h"
 #include "SkOpEdgeBuilder.h"
 #include "SkPathOpsCommon.h"
@@ skipping 28 matching lines @@
         if (!angle) {
             return nullptr;
         }
         if (winding == SK_MinS32) {
             continue;
         }
         int sumMiWinding, sumSuWinding;
         if (sortable) {
             segment = angle->segment();
             sumMiWinding = segment->updateWindingReverse(angle);
+            if (sumMiWinding == SK_MinS32) {
+                SkASSERT(segment->globalState()->debugSkipAssert());
+                return nullptr;
+            }
             sumSuWinding = segment->updateOppWindingReverse(angle);
+            if (sumSuWinding == SK_MinS32) {
+                SkASSERT(segment->globalState()->debugSkipAssert());
+                return nullptr;
+            }
             if (segment->operand()) {
                 SkTSwap<int>(sumMiWinding, sumSuWinding);
             }
         }
         SkOpSegment* first = nullptr;
         const SkOpAngle* firstAngle = angle;
         while ((angle = angle->next()) != firstAngle) {
             segment = angle->segment();
             SkOpSpanBase* start = angle->start();
             SkOpSpanBase* end = angle->end();
@@ skipping 395 matching lines @@
         one.dumpHex();
         SkDebugf("two: fill=%d\n", two.getFillType());
         two.dumpHex();
         SkASSERT(0);
     }
     return true;
 #else
     return OpDebug(one, two, op, result  SkDEBUGPARAMS(true) SkDEBUGPARAMS(nullptr));
 #endif
 }