[FIX] web: groupby product on package types triggers a js error

On a database where many modules are installed (e.g.  runbot all), with
the option "manage available packaging options per products", doing a groupby
"product" on the "package type" list view triggers a js error.
It comes from the fact that the fixed_group variable contains a "length"
attribute; the _().each function uses this to determine (erroneously)
that the object is an array.
It thus uses fixed_group[0] to get an undefined, and then tries to access
a method of undefined.

We replace the each by a simple js loop.

opw 1863576

addons/web/static/src/js/framework/data.js

@@ -261,14 +261,15 @@ var QueryGroup = Class.extend({
 
         var count_key = (grouping_fields[0] && grouping_fields[0].split(':')[0]) + '_count';
         var aggregates = {};
-        _(fixed_group).each(function (value, key) {
-            if (key.indexOf('__') === 0
+        for (var key in fixed_group) {
+            if (fixed_group.hasOwnProperty(key)) {
+                if (!(key.indexOf('__') === 0
                     || _.contains(grouping_fields, key)
-                    || (key === count_key)) {
-                return;
+                    || (key === count_key))) {
+                    aggregates[key] = fixed_group[key] || 0;
+                }
             }
-            aggregates[key] = value || 0;
-        });
+        }
 
         this.model = new Model(
             model, fixed_group.__context, fixed_group.__domain);