Fix memory leak in Imagick::colorThresholdImage()

imagick_class.c

@@ -13492,8 +13492,12 @@ PHP_METHOD(Imagick, colorThresholdImage)
 		return;
 
 	stop_color_wand = php_imagick_zval_to_pixelwand (stop_color_param, IMAGICK_CLASS, &stop_color_allocated TSRMLS_CC);
-	if (!stop_color_wand)
+	if (!stop_color_wand) {
+		if (start_color_allocated)
+			start_color_wand = DestroyPixelWand (start_color_wand);
+
 		return;
+	}
 
 	status = MagickColorThresholdImage(
 		intern->magick_wand,

package.xml

@@ -390,6 +390,7 @@ This extension requires ImageMagick version 6.5.3-10+ and PHP 5.6.0+.
 				<file name="310_Imagick_whiteBalanceImage.phpt" role="test" />
 				<file name="311_Imagick_channelFxImage.phpt" role="test" />
 				<file name="312_Imagick_colorThresholdImage.phpt" role="test" />
+				<file name="313_Imagick_colorThresholdImage_invalid.phpt" role="test" />
 				<file name="314_Imagick_getBackgroundColor.phpt" role="test" />
 				<file name="315_Imagick_getImageArtifacts.phpt" role="test" />
 				<file name="316_Imagick_getImageKurtosis.phpt" role="test" />

tests/313_Imagick_colorThresholdImage_invalid.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Test Imagick, colorThresholdImage invalid input
+--SKIPIF--
+<?php
+require_once(dirname(__FILE__) . '/skipif.inc');
+checkClassMethods('Imagick', array('colorThresholdImage'));
+?>
+--FILE--
+<?php
+
+function colorThresholdImage() {
+    $imagick = new \Imagick(__DIR__ . '/Biter_500.jpg');
+    try {
+        $imagick->colorThresholdImage(
+            "rgb(10, 10, 10)",
+            "complete garbage"
+        );
+    } catch (ImagickException $e) {
+        echo "ImagickException: ", $e->getMessage(), "\n";
+    }
+}
+
+colorThresholdImage() ;
+?>
+--EXPECTF--
+ImagickException: Unrecognized color string