Fixed a few places where uninitialized memory could have been read

src/effects/SkTileImageFilter.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 "SkTileImageFilter.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
@@ skipping 43 matching lines @@
     dstRect.offset(SkIntToScalar(localOffset.fX), SkIntToScalar(localOffset.fY));
     canvas.drawRect(dstRect, paint);
     *dst = device->accessBitmap(false);
     return true;
 }
 
 SkTileImageFilter::SkTileImageFilter(SkFlattenableReadBuffer& buffer)
   : INHERITED(1, buffer) {
     buffer.readRect(&fSrcRect);
     buffer.readRect(&fDstRect);
-    buffer.validate(SkIsValidRect(fSrcRect) && SkIsValidRect(fDstRect));
+    buffer.validate(buffer.isValid() && SkIsValidRect(fSrcRect) && SkIsValidRect(fDstRect));
 }
 
 void SkTileImageFilter::flatten(SkFlattenableWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
     buffer.writeRect(fSrcRect);
     buffer.writeRect(fDstRect);
 }