[FIX] bus, mail: navigate from tests with mocked bus services

Before this commit, when navigating from test environment (e.g.
page reload), it crashed with following error:

`TypeError: Cannot convert undefined or null to object`

This error comes from mocked bus services in tests: even when they
have been destroyed, they handle the window event 'unload'. They
no longer have a parented parent, so `this.call()` returns
`undefined`, hence the crash.

This commit prevents mocked bus services to listen on window 'unload'
event. Tests must always simulate this window event by explicitly
calling the handler.

closes odoo/odoo#41378

X-original-commit: fd08d04f0a24fea52e7b668b90aec48b33d349a3
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

addons/bus/static/src/js/crosstab_bus.js

@@ -109,7 +109,7 @@ var CrossTabBus = Longpolling.extend({
             peers[this._id] = new Date().getTime();
             this._callLocalStorage('setItem', 'peers', peers);
 
-            $(window).on('unload.' + this._id, this._onUnload.bind(this));
+            this._registerWindowUnload();
 
             if (!this._callLocalStorage('getItem', 'master')) {
                 this._startElection();
@@ -230,6 +230,12 @@ var CrossTabBus = Longpolling.extend({
 
         this._heartbeatTimeout = setTimeout(this._heartbeat.bind(this), hbPeriod);
     },
+    /**
+     * @private
+     */
+    _registerWindowUnload: function () {
+        $(window).on('unload.' + this._id, this._onUnload.bind(this));
+    },
     /**
      * Check with the local storage if the current tab is the master tab.
      * If this tab became the master, trigger 'become_master' event

addons/mail/static/tests/helpers/test_utils.js

@@ -59,6 +59,7 @@ var MockMailService = Class.extend({
     bus_service: function () {
         return BusService.extend({
             _poll: function () {}, // Do nothing
+            _registerWindowUnload: function () {}, // Do nothing
             isOdooFocused: function () { return true; },
             updateOption: function () {},
         });