Add unregisterGlobalEventHandlers method

And call it when `converse.initialize` gets called again

dist/converse.js

@@ -62948,6 +62948,12 @@ function finishInitialization() {
   }
 }
 
+function unregisterGlobalEventHandlers() {
+  document.removeEventListener("visibilitychange", _converse.saveWindowState);
+
+  _converse.emit('registeredGlobalEventHandlers');
+}
+
 function cleanup() {
   // Looks like _converse.initialized was called again without logging
   // out or disconnecting in the previous session.
@@ -62956,6 +62962,7 @@ function cleanup() {
 
   _converse.chatboxviews.closeAllChatBoxes();
 
+  unregisterGlobalEventHandlers();
   window.localStorage.clear();
   window.sessionStorage.clear();
 

src/headless/converse-core.js

@@ -433,12 +433,18 @@ function finishInitialization () {
 }
 
 
+function unregisterGlobalEventHandlers () {
+    document.removeEventListener("visibilitychange", _converse.saveWindowState);
+    _converse.emit('registeredGlobalEventHandlers');
+}
+
 function cleanup () {
     // 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.
     Backbone.history.stop();
     _converse.chatboxviews.closeAllChatBoxes();
+    unregisterGlobalEventHandlers();
     window.localStorage.clear();
     window.sessionStorage.clear();
     if (_converse.bookmarks) {