fix: type error in emote pack list in rooms with only non-default packs

If a room has emote packs, but none of them have an empty state key, we
insert 'null' to also add a default pack people can easily edit.
However, in that case we initialized the Map<String, Event?> variable
with a Map<String, Event>. As such assigning null will throw. Converting
manually with Map.of fixes that.

fixes #1138

lib/pages/settings_multiple_emotes/settings_multiple_emotes_view.dart

@@ -24,8 +24,11 @@ class MultipleEmotesSettingsView extends StatelessWidget {
       body: StreamBuilder(
         stream: room.onUpdate.stream,
         builder: (context, snapshot) {
-          final Map<String, Event?> packs =
-              room.states['im.ponies.room_emotes'] ?? <String, Event>{};
+          final packStateEvents = room.states['im.ponies.room_emotes'];
+          // we need to manually convert the map using Map.of, otherwise assigning null will throw a type error.
+          final Map<String, Event?> packs = packStateEvents != null
+              ? Map<String, Event?>.of(packStateEvents)
+              : <String, Event?>{};
           if (!packs.containsKey('')) {
             packs[''] = null;
           }