add test

Author: devnexen

ext/gd/tests/gh20551.phpt

@@ -0,0 +1,22 @@
+--TEST--
+GH-20551: (imagegammacorrect out of range input/output value)
+--EXTENSIONS--
+gd
+--FILE--
+<?php
+$im = imagecreate(64, 32);
+
+try {
+	imagegammacorrect($im, NAN, 1.0);
+} catch (\ValueError $e) {
+	echo $e->getMessage(), PHP_EOL;
+}
+try {
+	imagegammacorrect($im, -NAN, 1.0);
+} catch (\ValueError $e) {
+	echo $e->getMessage(), PHP_EOL;
+}
+?>
+--EXPECT--
+An input divided by an output must be finite
+An input divided by an output must be finite