converse-core: Call _tearDown when initialized again

When it's clear that a previous teardown didn't happen.
So that objects can be garbage collected and that obsolete event handlers don't
fire anymore.

src/converse-core.js

@@ -134,6 +134,15 @@
         settings = typeof settings !== "undefined" ? settings : {};
         var init_deferred = new $.Deferred();
         var converse = this;
+
+        if (typeof converse.chatboxes !== 'undefined') {
+            // Looks like converse.initialized was called again without logging
+            // out or disconnecting in the previous session.
+            // This happens in tests.
+            // We therefore first clean up.
+            converse._tearDown();
+        }
+
         var unloadevent;
         if ('onpagehide' in window) {
             // Pagehide gets thrown in more cases than unload. Specifically it