[libfuzzer] improving gfx_png_image_fuzzer

testing/libfuzzer/fuzzers/gfx_png_image_fuzzer.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "ui/gfx/image/image.h"
 
 // Entry point for LibFuzzer.
 extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
-  gfx::Image::CreateFrom1xPNGBytes(data, size);
+  gfx::Image image = gfx::Image::CreateFrom1xPNGBytes(data, size);
+
+  if (image.IsEmpty())
+    return 0;
+
+  image.ToSkBitmap();
+
   return 0;
 }