fix one more fuzzer

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 846 matching lines @@
         s1 = overS->find(seg1o);
         e1 = overE->find(seg1o);
         FAIL_IF(!s1);
         FAIL_IF(!e1);
         if (!s1->starter(e1)->span()->upCast()->windValue()) {
             return true;
         }
     }
     const SkOpPtT* s2 = overS->find(seg2);
     const SkOpPtT* e2 = overE->find(seg2);
+    FAIL_IF(!s2);
     FAIL_IF(!e2);
     if (!s2->starter(e2)->span()->upCast()->windValue()) {
         s2 = overS->find(seg2o);
         e2 = overE->find(seg2o);
         FAIL_IF(!s2);
         FAIL_IF(!e2);
         if (!s2->starter(e2)->span()->upCast()->windValue()) {
             return true;
         }
     }
@@ skipping 507 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()));
 }