SkCodec::onGetScanlineDecoder must call rewind.

src/codec/SkCodec.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 "SkCodec.h"
 #include "SkData.h"
 #include "SkCodec_libbmp.h"
@@ skipping 70 matching lines @@
     const bool needsRewind = fNeedsRewind;
     fNeedsRewind = true;
     if (!needsRewind) {
         return kNoRewindNecessary_RewindState;
     }
     return fStream->rewind() ? kRewound_RewindState
                              : kCouldNotRewind_RewindState;
 }
 
 SkScanlineDecoder* SkCodec::getScanlineDecoder(const SkImageInfo& dstInfo) {
-    fScanlineDecoder.reset(NULL);
-    if (!rewindIfNeeded()) {
-        return NULL;
-    }
     fScanlineDecoder.reset(this->onGetScanlineDecoder(dstInfo));
     return fScanlineDecoder.get();
 }