Remove useless conversation icon in tablet mode

lib/ui/widgets/conversation_image_widget.dart

@@ -15,6 +15,7 @@ class ConversationImageWidget extends StatelessWidget {
   final UsersList users;
   final double size;
   final Group group;
+  final bool noUserImage;
 
   const ConversationImageWidget({
     Key key,
@@ -22,6 +23,7 @@ class ConversationImageWidget extends StatelessWidget {
     @required this.users,
     this.group,
     this.size = 30,
+    this.noUserImage,
   })  : assert(conversation != null),
         assert(users != null),
         assert(size > 0),
@@ -30,6 +32,7 @@ class ConversationImageWidget extends StatelessWidget {
   @override
   Widget build(BuildContext context) => Material(
         child: _buildIcon(),
+        color: Colors.transparent,
         borderRadius: BorderRadius.all(
           Radius.circular(18.0),
         ),
@@ -50,6 +53,8 @@ class ConversationImageWidget extends StatelessWidget {
       );
     }
 
+    if (noUserImage == true) return Container(width: size);
+
     if (conversation.members.length < 2)
       return Icon(
         Icons.lock,

lib/ui/widgets/tablet_mode/memberships_panel.dart

@@ -222,6 +222,7 @@ class _MembershipsPanelState extends SafeState<MembershipsPanel> {
         leading: ConversationImageWidget(
           conversation: conversation,
           users: _usersList,
+          noUserImage: conversation.isGroupConversation,
         ),
         title: Row(
           children: [