[FIX] py.js: arguments dispatching in PY_call

When providing an args of ``null`` (or ``undefined``) and a non-empty
kwargs, the kwargs would be removed/ignored.

While explicitly providing a null args is not necessary, it's perfectly
valid.

addons/web/static/lib/py.js/lib/py.js

@@ -547,11 +547,13 @@ var py = {};
     };
     py.PY_call = function (callable, args, kwargs) {
         if (!args) {
-            args = []; kwargs = {};
-        } else if (typeof args === 'object' && !(args instanceof Array)) {
+            args = [];
+        }
+        if (typeof args === 'object' && !(args instanceof Array)) {
             kwargs = args;
             args = [];
-        } else if (!kwargs) {
+        }
+        if (!kwargs) {
             kwargs = {};
         }
         if (callable.__is_type) {