Sync with upstream

Even though libgd/libgd#492 is not a relevant bug fix for PHP, since
the binding doesn't use the `gdImage*Ptr()` functions at all, we're
porting the fix to stay in sync here.
void term_source (j_decompress_ptr cinfo)
{
#if 0
	* never used */
	my_src_ptr src = (my_src_ptr) cinfo->src;
#endif
}

void term_source (j_decompress_ptr cinfo)
{
#if 0
	* never used */
	my_src_ptr src = (my_src_ptr) cinfo->src;
#endif
}
