[Client] Fix spurious server room join error

The server replies RespContextError when a join command is received for a
room that connection is already registered in. The client was sending such
duplicate joins in benign situations - double-clicking to join a room, or
clicking a room the selector was already auto-joining - and answered them
with a modal telling users to restart the client.

Joins for the same room are now deduplicated while one is in flight, and a
remaining RespContextError is healed by leaving and rejoining the room so
the tab appears without a client restart. Error dialogs are only shown for
user-initiated joins, so failed auto-joins no longer spam critical popups.

cockatrice/src/interface/widgets/tabs/tab_server.h

@@ -10,6 +10,7 @@
 #include "tab.h"
 
 #include <QGroupBox>
+#include <QMap>
 #include <QTextBrowser>
 #include <QTreeWidget>
 
@@ -58,10 +59,14 @@ private slots:
                           int roomId);
 
 private:
+    void leaveAndRejoinRoom(int roomId, bool setCurrent);
+
     AbstractClient *client;
     RoomSelector *roomSelector;
     QTextBrowser *serverInfoBox;
     bool shouldEmitUpdate = false;
+    /** Room ids with a join command in flight, mapped to whether the tab should be focused once it opens. */
+    QMap<int, bool> pendingRoomJoins;
 
 public:
     TabServer(TabSupervisor *_tabSupervisor, AbstractClient *_client);