Fixing crash found by fuzzer

src/core/SkMallocPixelRef.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 "SkMallocPixelRef.h"
 #include "SkBitmap.h"
 #include "SkFlattenableBuffers.h"
@@ skipping 124 matching lines @@
     if (fCTable) {
         fCTable->writeToBuffer(buffer);
     }
 }
 
 SkMallocPixelRef::SkMallocPixelRef(SkFlattenableReadBuffer& buffer)
     : INHERITED(buffer, NULL)
     , fOwnPixels(true)
 {
     fRB = buffer.read32();
-    size_t size = this->info().getSafeSize(fRB);
+    size_t size = buffer.isValid() ? this->info().getSafeSize(fRB) : 0;
     if (buffer.validateAvailable(size)) {
         fStorage = sk_malloc_throw(size);
         buffer.readByteArray(fStorage, size);
     } else {
         fStorage = NULL;
     }
 
     if (buffer.readBool()) {
         fCTable = SkNEW_ARGS(SkColorTable, (buffer));
     } else {
         fCTable = NULL;
     }
 
     this->setPreLocked(fStorage, fCTable);
 }