Fix crash when navigating too quickly in double screened views on IPAD

Classes/ChatsListView.m

@@ -43,6 +43,7 @@
 	[super viewWillDisappear:animated];
 
 	[NSNotificationCenter.defaultCenter removeObserver:self name:kLinphoneMessageReceived object:nil];
+	self.view = NULL;
 }
 
 #pragma mark - Event Functions

Classes/HistoryListView.m

@@ -63,6 +63,10 @@ static UICompositeViewDescription *compositeDescription = nil;
 	[NSNotificationCenter.defaultCenter postNotificationName:kLinphoneCallUpdate object:self];
 }
 
+- (void) viewWillDisappear:(BOOL)animated {
+	self.view = NULL;
+}
+
 #pragma mark -
 
 - (void)changeView:(HistoryView)view {