Upstream fix from https://bitbucket.org/libgd/gd-libgd/issue/75
Merge branch 'PHP-5.5'

* PHP-5.5:
  Upstream fix from https://bitbucket.org/libgd/gd-libgd/issue/75
Use same logic to load WebP image that other formats
Merge branch 'PHP-5.5'

* PHP-5.5:
  Use same logic to load WebP image that other formats