Add workaround for delegate stuck transition bug

Sometimes and randomly, a HListView/HGridView delegate's
add/populate transition will stop before completion.

This especially happens on startup when loading a large room list,
one room might get stuck and left tiny or invisible, despite its
normal space still being taken.

src/gui/MainPane/AccountDelegate.qml

@@ -243,4 +243,6 @@ HTile {
         sequences: window.settings.keys.togglePresenceOffline
         onActivated: account.togglePresence("offline")
     }
+
+    DelegateTransitionFixer {}
 }

src/gui/MainPane/RoomDelegate.qml

@@ -207,6 +207,8 @@ HTile {
         if (loadEventsFutureId) py.cancelCoro(loadEventsFutureId)
     }
 
+    DelegateTransitionFixer {}
+
     Timer {
         interval: 1000
         triggeredOnStart: true