Fix GH-17703: imagescale both width and heigh set with negative values.

Throwing a ValueError in this particular case.

Author: devnexen

ext/gd/gd.c

@@ -3633,6 +3633,11 @@ PHP_FUNCTION(imagescale)
 
 	im = php_gd_libgdimageptr_from_zval_p(IM);
 
+	if (tmp_h < 0 && tmp_w < 0) {
+		zend_value_error("$width and $height cannot be both negative");
+		RETURN_THROWS();
+	}
+
 	if (tmp_h < 0 || tmp_w < 0) {
 		/* preserve ratio */
 		long src_x, src_y;

ext/gd/tests/gh17703.phpt

@@ -0,0 +1,17 @@
+--TEST--
+GH-17703 both width and height value being negative triggers ValueError on width.
+--EXTENSIONS--
+gd
+--FILE--
+<?php
+
+$img = imagecreatetruecolor ( 256, 1);
+
+try {
+	imagescale($img, -1, -1, 0);
+} catch (\ValueError $e) {
+	echo $e->getMessage();
+}
+?>
+--EXPECT--
+$width and $height cannot be both negative