Fix potential bugs without expected behavior change

- Fix uninitialized variables
- Fix potentially not set variables
- Fix wrong parameter default value
- Fix method scope
- Fix missing return value

mod/help.php

@@ -33,6 +33,7 @@ function help_content(App $a)
 	Nav::setSelected('help');
 
 	$text = '';
+	$filename = '';
 
 	if ($a->argc > 1) {
 		$path = '';