Fix #340: System frozen

gdImageCreate() doesn't check for oversized images and as such is prone
to DoS vulnerabilities. We fix that by applying the same overflow check
that is already in place for gdImageCreateTrueColor().

CVE-2016-9317
void gd_error_ex(int priority, const char *format, ...)
{
	va_list args;

	va_start(args, format);
	_gd_error_ex(priority, format, args);
	va_end(args);
}

void gd_error_ex(int priority, const char *format, ...)
{
	va_list args;

	va_start(args, format);
	_gd_error_ex(priority, format, args);
	va_end(args);
}
