reduce this in block scopes (#2526)

fixes #2455

lib/ast.js

@@ -313,9 +313,9 @@ var AST_Scope = DEFNODE("Scope", "variables functions uses_with uses_eval parent
         enclosed: "[SymbolDef*/S] a list of all symbol definitions that are accessed from this scope or any subscopes",
         cname: "[integer/S] current index for mangling variables (used internally by the mangler)",
     },
-    get_defun_scope: function () {
+    get_defun_scope: function() {
         var self = this;
-        while (self.is_block_scope() && self.parent_scope) {
+        while (self.is_block_scope()) {
             self = self.parent_scope;
         }
         return self;