imageloadfont: Perform overflow check before calculation

Instead of afterwards...

Author: nikic

ext/gd/gd.c

@@ -1443,6 +1443,13 @@ PHP_FUNCTION(imageloadfont)
 body_size_check = php_stream_tell(stream) - hdr_size;
 php_stream_seek(stream, i, SEEK_SET);
 
+if (overflow2(font->nchars, font->h) || overflow2(font->nchars * font->h, font->w )) {
+php_error_docref(NULL, E_WARNING, "Error reading font, invalid font header");
+efree(font);
+php_stream_close(stream);
+RETURN_FALSE;
+}
+
 body_size = font->w * font->h * font->nchars;
 if (body_size != body_size_check) {
 font->w = FLIPWORD(font->w);
@@ -1451,13 +1458,6 @@ PHP_FUNCTION(imageloadfont)
 body_size = font->w * font->h * font->nchars;
 }
 
-if (overflow2(font->nchars, font->h) || overflow2(font->nchars * font->h, font->w )) {
-php_error_docref(NULL, E_WARNING, "Error reading font, invalid font header");
-efree(font);
-php_stream_close(stream);
-RETURN_FALSE;
-}
-
 if (body_size != body_size_check) {
 php_error_docref(NULL, E_WARNING, "Error reading font");
 efree(font);