fix fuzz bug

src/pathops/SkPathOpsTSect.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkPathOpsTSect_DEFINED
 #define SkPathOpsTSect_DEFINED
 
 #include "SkChunkAlloc.h"
@@ skipping 1141 matching lines @@
             this->removeSpan(test);
         }
     }
 }
 
 template<typename TCurve, typename OppCurve>
 SkTSpan<TCurve, OppCurve>* SkTSect<TCurve, OppCurve>::extractCoincident(
         SkTSect<OppCurve, TCurve>* sect2,
         SkTSpan<TCurve, OppCurve>* first, SkTSpan<TCurve, OppCurve>* last) {
     first = findCoincidentRun(first, &last);
-    if (!first) {
+    if (!first || !last) {
         return nullptr;
     }
     // march outwards to find limit of coincidence from here to previous and next spans
     double startT = first->fStartT;
     double oppStartT SK_INIT_TO_AVOID_WARNING;
     double oppEndT SK_INIT_TO_AVOID_WARNING;
     SkTSpan<TCurve, OppCurve>* prev = first->fPrev;
     SkASSERT(first->fCoinStart.isCoincident());
     SkTSpan<OppCurve, TCurve>* oppFirst = first->findOppT(first->fCoinStart.perpT());
     SkOPASSERT(last->fCoinEnd.isCoincident());
@@ skipping 1122 matching lines @@
             --last;
         } else {
             intersections->setCoincident(index++);
         }
         intersections->setCoincident(index);
     }
     SkASSERT(intersections->used() <= TCurve::kMaxIntersections);
 }
 
 #endif