[libfuzzer] Prevent division by zero in libpng_read_fuzzer.

testing/libfuzzer/fuzzers/libpng_read_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 <vector>
 
 #include "base/bind.h"
@@ skipping 74 matching lines @@
   int bit_depth, color_type, interlace_type, compression_type;
   int filter_type;
 
   if (!png_get_IHDR(png_ptr, info_ptr, &width, &height,
         &bit_depth, &color_type, &interlace_type,
         &compression_type, &filter_type)) {
     return 0;
   }
 
   // This is going to be too slow.
-  if (height > 100000000 / width)
+  if (width && height > 100000000 / width)

[aizatsky, 2016/03/18 17:18:18]

Is this written to prevent overflow? width * height > ... would look much nicer.

[mmoroz, 2016/03/21 09:07:37]

Yes, this is for overflow prevention (from here:
https://codereview.chromium.org/1808123004/).
I can replace it with cast to uint64_t, if you think it would be better.

     return 0;
 
   int passes = png_set_interlace_handling(png_ptr);
   png_start_read_image(png_ptr);
 
   for (int pass = 0; pass < passes; ++pass) {
     for (png_uint_32 y = 0; y < height; ++y) {
       png_read_row(png_ptr, static_cast<png_bytep>(row), NULL);
     }
   }
 
   return 0;
 }