Prevent infinite loop caused when argv not set.

If shell is invoked with the wrong PHP executable (not CLI) and argv is not an array,  array_search on null causes infinite number of error messages.

lib/Cake/Console/ShellDispatcher.php

@@ -323,6 +323,7 @@ class ShellDispatcher {
 	protected function _parsePaths($args) {
 		$parsed = array();
 		$keys = array('-working', '--working', '-app', '--app', '-root', '--root');
+		$args = (array)$args;
 		foreach ($keys as $key) {
 			while (($index = array_search($key, $args)) !== false) {
 				$keyname = str_replace('-', '', $key);