only call exec() if allowed to

settings/admin.php

@@ -101,9 +101,11 @@ $tmpl->printPage();
  * @return null|string
  */
 function findBinaryPath($program) {
+	if (OC_Helper::is_function_enabled('exec')) {
 		exec('command -v ' . escapeshellarg($program) . ' 2> /dev/null', $output, $returnCode);
 		if ($returnCode === 0 && count($output) > 0) {
 			return escapeshellcmd($output[0]);
 		}
+	}
 	return null;
 }