Fix space switching on mobile

We forgot to connect to onTapped on the touchscreen-specific TapHandler.
I also needed to carve out a specific case for DMs so it doesn't try to
resolve the non-existent "DM" resource.

src/app/qml/AvatarTabButton.qml

@@ -48,6 +48,7 @@ Delegates.RoundedItemDelegate {
 
     TapHandler {
         acceptedDevices: PointerDevice.TouchScreen
+        onTapped: root.selected()
         onLongPressed: root.contextMenuRequested()
     }
 

src/app/roommanager.cpp

@@ -540,7 +540,9 @@ void RoomManager::setCurrentSpace(const QString &spaceId, bool setRoom)
 
         const auto &lastRoom = m_lastRoomConfig.readEntry(configSpaceId, QString());
         if (lastRoom.isEmpty()) {
-            resolveResource(spaceId, "no_join"_L1);
+            if (spaceId != u"DM"_s) {
+                resolveResource(spaceId, "no_join"_L1);
+            }
         } else {
             resolveResource(lastRoom, "no_join"_L1);
         }