refactor: Use correct Matrix instance

lib/pages/chat/chat_input_row.dart

@@ -215,9 +215,9 @@ class ChatInputRow extends StatelessWidget {
                   ),
                 ),
               ),
-              if (controller.matrix!.isMultiAccount &&
-                  controller.matrix!.hasComplexBundles &&
-                  controller.matrix!.currentBundle!.length > 1)
+              if (Matrix.of(context).isMultiAccount &&
+                  Matrix.of(context).hasComplexBundles &&
+                  Matrix.of(context).currentBundle!.length > 1)
                 Container(
                   height: 56,
                   alignment: Alignment.center,
@@ -279,8 +279,9 @@ class _ChatAccountPicker extends StatelessWidget {
 
   const _ChatAccountPicker(this.controller, {Key? key}) : super(key: key);
 
-  void _popupMenuButtonSelected(String mxid) {
-    final client = controller.matrix!.currentBundle!
+  void _popupMenuButtonSelected(String mxid, BuildContext context) {
+    final client = Matrix.of(context)
+        .currentBundle!
         .firstWhere((cl) => cl!.userID == mxid, orElse: () => null);
     if (client == null) {
       Logs().w('Attempted to switch to a non-existing client $mxid');
@@ -291,14 +292,13 @@ class _ChatAccountPicker extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    controller.matrix ??= Matrix.of(context);
     final clients = controller.currentRoomBundle;
     return Padding(
       padding: const EdgeInsets.all(8.0),
       child: FutureBuilder<Profile>(
         future: controller.sendingClient!.fetchOwnProfile(),
         builder: (context, snapshot) => PopupMenuButton<String>(
-          onSelected: _popupMenuButtonSelected,
+          onSelected: (mxid) => _popupMenuButtonSelected(mxid, context),
           itemBuilder: (BuildContext context) => clients
               .map(
                 (client) => PopupMenuItem<String>(
@@ -322,7 +322,7 @@ class _ChatAccountPicker extends StatelessWidget {
           child: Avatar(
             mxContent: snapshot.data?.avatarUrl,
             name: snapshot.data?.displayName ??
-                controller.matrix!.client.userID!.localpart,
+                Matrix.of(context).client.userID!.localpart,
             size: 20,
           ),
         ),