ensure that we call onUnlock only when we onLock succeeded

src/core/SkPixelRef.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkPixelRef.h"
 #include "SkFlattenableBuffers.h"
 #include "SkThread.h"
@@ skipping 160 matching lines @@
 }
 
 void SkPixelRef::lockPixels() {
     SkASSERT(!fPreLocked || SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount);
 
     if (!fPreLocked) {
         SkAutoMutexAcquire  ac(*fMutex);
 
         if (1 == ++fLockCount) {
             fPixels = this->onLockPixels(&fColorTable);
+            // If onLockPixels failed, it will return NULL
+            if (NULL == fPixels) {
+                fColorTable = NULL;
+            }
         }
     }
 }
 
 void SkPixelRef::unlockPixels() {
     SkASSERT(!fPreLocked || SKPIXELREF_PRELOCKED_LOCKCOUNT == fLockCount);
 
     if (!fPreLocked) {
         SkAutoMutexAcquire  ac(*fMutex);
 
         SkASSERT(fLockCount > 0);
         if (0 == --fLockCount) {
-            this->onUnlockPixels();
-            fPixels = NULL;
-            fColorTable = NULL;
+            // don't call onUnlockPixels unless onLockPixels succeeded
+            if (fPixels) {
+                this->onUnlockPixels();
+                fPixels = NULL;
+                fColorTable = NULL;
+            } else {
+                SkASSERT(NULL == fColorTable);
+            }
         }
     }
 }
 
 bool SkPixelRef::lockPixelsAreWritable() const {
     return this->onLockPixelsAreWritable();
 }
 
 bool SkPixelRef::onLockPixelsAreWritable() const {
     return true;
@@ skipping 69 matching lines @@
 
 #ifdef SK_BUILD_FOR_ANDROID
 void SkPixelRef::globalRef(void* data) {
     this->ref();
 }
 
 void SkPixelRef::globalUnref() {
     this->unref();
 }
 #endif