disallow -4 pointer

src/core/SkPathRef.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBuffer.h"
 #include "SkOnce.h"
 #include "SkPath.h"
@@ skipping 601 matching lines @@
 }
 
 SkPathRef::Iter::Iter(const SkPathRef& path) {
     this->setPathRef(path);
 }
 
 void SkPathRef::Iter::setPathRef(const SkPathRef& path) {
     fPts = path.points();
     fVerbs = path.verbs();
     fVerbStop = path.verbsMemBegin();
-    fConicWeights = path.conicWeights() - 1; // begin one behind
+    fConicWeights = path.conicWeights();
+    if (fConicWeights) {
+      fConicWeights -= 1;  // begin one behind
+    }
 }
 
 uint8_t SkPathRef::Iter::next(SkPoint pts[4]) {
     SkASSERT(pts);
     if (fVerbs == fVerbStop) {
         return (uint8_t) SkPath::kDone_Verb;
     }
 
     // fVerbs points one beyond next verb so decrement first.
     unsigned verb = *(--fVerbs);
@@ skipping 116 matching lines @@
                 break;
             default:
                 SkDEBUGFAIL("Unknown Verb");
                 break;
         }
     }
     SkASSERT(mask == fSegmentMask);
 #endif // SK_DEBUG_PATH
 }
 #endif