Fix conditional check when copying coverage stages in ODS

src/gpu/GrOptDrawState.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrOptDrawState.h"
 
 #include "GrDrawState.h"
@@ skipping 51 matching lines @@
 
     // Copy Color Stages from DS to ODS
     if (firstColorStageIdx < drawState.numColorStages()) {
         fColorStages.reset(&drawState.getColorStage(firstColorStageIdx),
                            drawState.numColorStages() - firstColorStageIdx);
     } else {
         fColorStages.reset();
     }
 
     // Copy Coverage Stages from DS to ODS
-    if (drawState.numCoverageStages() > 0 && separateCoverageFromColor) {
+    if (firstCoverageStageIdx < drawState.numCoverageStages() && separateCoverageFromColor) {
         fCoverageStages.reset(&drawState.getCoverageStage(firstCoverageStageIdx),
                               drawState.numCoverageStages() - firstCoverageStageIdx);
     } else {
         fCoverageStages.reset();
-        if (drawState.numCoverageStages() > 0) {
+        if (firstCoverageStageIdx < drawState.numCoverageStages()) {
             // TODO: Once we have flag to know if we only multiply on stages, only push coverage
             // into color stages if everything is multiply
             fColorStages.push_back_n(drawState.numCoverageStages() - firstCoverageStageIdx,
                                      &drawState.getCoverageStage(firstCoverageStageIdx));
         }
     }
 };
 
 GrOptDrawState* GrOptDrawState::Create(const GrDrawState& drawState, const GrDrawTargetCaps& caps,
                                        GrGpu::DrawType drawType) {
@@ skipping 292 matching lines @@
         }
     }
 
     SkASSERT(0 == memcmp(this->fFixedFunctionVertexAttribIndices,
                          that.fFixedFunctionVertexAttribIndices,
                          sizeof(this->fFixedFunctionVertexAttribIndices)));
 
     return true;
 }