Fix for rare crash in Poly::addEdge().

src/gpu/GrTessellator.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 "GrTessellator.h"
 
 #include "GrPathUtils.h"
@@ skipping 400 matching lines @@
                e->fTop->fPoint.fX, e->fTop->fPoint.fY, e->fBottom->fPoint.fX, e->fBottom->fPoint.fY,
                fID, side == kLeft_Side ? "left" : "right");
         Poly* partner = fPartner;
         Poly* poly = this;
         if (partner) {
             fPartner = partner->fPartner = nullptr;
         }
         if (!fTail) {
             fHead = fTail = ALLOC_NEW(MonotonePoly, (e, side), alloc);
             fCount += 2;
+        } else if (e->fBottom == fTail->fLastEdge->fBottom) {
+            return poly;
         } else if (side == fTail->fSide) {
             fTail->addEdge(e);
             fCount++;
         } else {
-            if (e->fBottom == fTail->fLastEdge->fBottom) {
-                return poly;
-            }
             e = ALLOC_NEW(Edge, (fTail->fLastEdge->fBottom, e->fBottom, 1), alloc);
             fTail->addEdge(e);
             fCount++;
             if (partner) {
                 partner->addEdge(e, side, alloc);
                 poly = partner;
             } else {
                 MonotonePoly* m = ALLOC_NEW(MonotonePoly, (e, side), alloc);
                 m->fPrev = fTail;
                 fTail->fNext = m;
@@ skipping 795 matching lines @@
             if (!v->fFirstEdgeBelow) {
                 if (leftPoly && rightPoly && leftPoly != rightPoly) {
                     SkASSERT(leftPoly->fPartner == nullptr && rightPoly->fPartner == nullptr);
                     rightPoly->fPartner = leftPoly;
                     leftPoly->fPartner = rightPoly;
                 }
             }
         }
         if (v->fFirstEdgeBelow) {
             if (!v->fFirstEdgeAbove) {
-                if (leftPoly) {
+                if (leftPoly && rightPoly) {
                     if (leftPoly == rightPoly) {
                         if (leftPoly->fTail && leftPoly->fTail->fSide == Poly::kLeft_Side) {
                             leftPoly = new_poly(&polys, leftPoly->lastVertex(),
                                                  leftPoly->fWinding, alloc);
                             leftEnclosingEdge->fRightPoly = leftPoly;
                         } else {
                             rightPoly = new_poly(&polys, rightPoly->lastVertex(),
                                                  rightPoly->fWinding, alloc);
                             rightEnclosingEdge->fLeftPoly = rightPoly;
                         }
@@ skipping 188 matching lines @@
         }
     }
     int actualCount = static_cast<int>(vertsEnd - *verts);
     SkASSERT(actualCount <= count);
     SkASSERT(pointsEnd - points == actualCount);
     delete[] points;
     return actualCount;
 }
 
 } // namespace