Port "gd2: use existing overflow2() rather than ad-hoc version" (#15090)

We port this modification[1] from libgd into our bundled libgd, because
the change makes sense, and we want the code bases to stay in sync as
close as possible.

We also apply a quick fix to the respective test.

[1] <libgd/libgd@f0a059b>

Author: cmb69

ext/gd/libgd/gd_gd2.c

@@ -137,7 +137,7 @@ static int _gd2GetHeader(gdIOCtxPtr in, int *sx, int *sy, int *cs, int *vers, in
 	GD2_DBG(gd_error("%d Chunks vertically", *ncy));
 
 	if (gd2_compressed(*fmt)) {
-		if (*ncx <= 0 || *ncy <= 0 || *ncx > INT_MAX / *ncy) {
+		if (overflow2(*ncx, *ncy)) {
 			GD2_DBG(printf ("Illegal chunk counts: %d * %d\n", *ncx, *ncy));
 			goto fail1;
 		}

ext/gd/tests/bug73869.phpt

@@ -14,8 +14,10 @@ var_dump(imagecreatefromgd2(__DIR__ . DIRECTORY_SEPARATOR . 'bug73869a.gd2'));
 var_dump(imagecreatefromgd2(__DIR__ . DIRECTORY_SEPARATOR . 'bug73869b.gd2'));
 ?>
 --EXPECTF--
+%A
 Warning: imagecreatefromgd2(): "%s" is not a valid GD2 file in %s on line %d
 bool(false)
 
+%A
 Warning: imagecreatefromgd2(): "%s" is not a valid GD2 file in %s on line %d
 bool(false)