fix fuzz bug

src/pathops/SkOpCoincidence.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkOpCoincidence.h"
 #include "SkOpSegment.h"
 #include "SkPathOpsTSect.h"
 
@@ skipping 676 matching lines @@
     if (oeExisting && (oeExisting == os || oeExisting->contains(osExisting ? osExisting : os))) {
         return false;
     }
     // extra line in debug code
     this->debugValidate();
     if (!cs || !os) {
         SkOpPtT* csWritable = cs ? const_cast<SkOpPtT*>(cs)
             : coinSeg->addT(coinTs, SkOpSegment::kNoAliasMatch, nullptr);
         SkOpPtT* osWritable = os ? const_cast<SkOpPtT*>(os)
             : oppSeg->addT(oppTs, SkOpSegment::kNoAliasMatch, nullptr);
-        if (!osWritable) {
+        if (!csWritable || !osWritable) {
             return false;
         }
         csWritable->span()->addOppAndMerge(osWritable->span());
         cs = csWritable;
         os = osWritable;
         if ((ce && ce->deleted()) || (oe && oe->deleted())) {
             return false;
         }
     }
     if (!ce || !oe) {
@@ skipping 764 matching lines @@
             this->release(fHead, coin);
         }
     } while ((coin = coin->next()));
 }
 
 bool SkOpCoincidence::testForCoincidence(const SkCoincidentSpans* outer, const SkOpPtT* testS,
         const SkOpPtT* testE) const {
     return testS->segment()->testForCoincidence(testS, testE, testS->span(),
             testE->span(), outer->coinPtTStart()->segment());
 }