fix another fuzz

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 824 matching lines @@
     } while ((outer = outer->next()));
     this->restoreHead();
     return true;
 }
 
 bool SkOpCoincidence::addOverlap(const SkOpSegment* seg1, const SkOpSegment* seg1o,
         const SkOpSegment* seg2, const SkOpSegment* seg2o,
         const SkOpPtT* overS, const SkOpPtT* overE) {
     const SkOpPtT* s1 = overS->find(seg1);
     const SkOpPtT* e1 = overE->find(seg1);
+    FAIL_IF(!s1);
     FAIL_IF(!e1);
     if (!s1->starter(e1)->span()->upCast()->windValue()) {
         s1 = overS->find(seg1o);
         e1 = overE->find(seg1o);
         FAIL_IF(!s1);
         FAIL_IF(!e1);
         if (!s1->starter(e1)->span()->upCast()->windValue()) {
             return true;
         }
     }
@@ skipping 505 matching lines @@
     }
     do {
         if (coin->coinPtTStart()->segment() == deleted
                 || coin->coinPtTEnd()->segment() == deleted
                 || coin->oppPtTStart()->segment() == deleted
                 || coin->oppPtTEnd()->segment() == deleted) {
             this->release(fHead, coin);
         }
     } while ((coin = coin->next()));
 }