Improve call membership tile

lib/ui/widgets/tablet_mode/memberships_panel.dart

@@ -167,13 +167,20 @@ class _MembershipsPanelState extends SafeState<MembershipsPanel> {
           : (conversation.sawLastMessage ? null : Color(0xFF1c443a)),
       child: ListTile(
         dense: true,
-        leading: Icon(conversation.isHavingCall ? Icons.phone : Icons.message),
+        leading: Icon(Icons.message),
         title: Text(
             ConversationsHelper.getConversationName(conversation, _usersList)),
         subtitle: Text(diffTimeFromNowToStr(membership.lastActive) +
             (conversation.isHavingCall ? "\n" + tr("Ongoing call") : "")),
         onTap: () =>
             MainController.of(context).openConversation(conversation.id),
+        trailing: conversation.isHavingCall
+            ? FloatingActionButton(
+                child: Icon(Icons.call),
+                onPressed: () =>
+                    MainController.of(context).startCall(conversation.id),
+              )
+            : null,
       ),
     );
   }