Check pixelRef before attempting to ktx encode.

src/images/SkImageDecoder_ktx.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 "SkColorPriv.h"
 #include "SkImageDecoder.h"
 #include "SkPixelRef.h"
@@ skipping 191 matching lines @@
 class SkKTXImageEncoder : public SkImageEncoder {
 protected:
     virtual bool onEncode(SkWStream* stream, const SkBitmap& bm, int quality) SK_OVERRIDE;
 
 private:
     virtual bool encodePKM(SkWStream* stream, const SkData *data);
     typedef SkImageEncoder INHERITED;
 };
 
 bool SkKTXImageEncoder::onEncode(SkWStream* stream, const SkBitmap& bitmap, int) {
+    if (!bitmap.pixelRef()) {
+        return false;
+    }
     SkAutoDataUnref data(bitmap.pixelRef()->refEncodedData());
 
     // Is this even encoded data?
     if (NULL != data) {
         const uint8_t *bytes = data->bytes();
         if (etc1_pkm_is_valid(bytes)) {
             return this->encodePKM(stream, data);
         }
 
         // Is it a KTX file??
@@ skipping 46 matching lines @@
     return SkImageDecoder::kUnknown_Format;
 }
 
 SkImageEncoder* sk_libktx_efactory(SkImageEncoder::Type t) {
     return (SkImageEncoder::kKTX_Type == t) ? SkNEW(SkKTXImageEncoder) : NULL;
 }
 
 static SkImageDecoder_DecodeReg gReg(sk_libktx_dfactory);
 static SkImageDecoder_FormatReg gFormatReg(get_format_ktx);
 static SkImageEncoder_EncodeReg gEReg(sk_libktx_efactory);