[Client] Directchatroom should exist

lib/src/Client.dart

@@ -123,12 +123,14 @@ class Client {
 
   /// Returns the (first) room ID from the store which is a private chat with the user [userId].
   /// Returns null if there is none.
-  String getDirectChatFromUserId(String userId) =>
-      accountData["m.direct"] != null &&
-              accountData["m.direct"].content[userId] is List<dynamic> &&
-              accountData["m.direct"].content[userId].length > 0
-          ? accountData["m.direct"].content[userId][0]
-          : null;
+  String getDirectChatFromUserId(String userId) => accountData["m.direct"] !=
+              null &&
+          accountData["m.direct"].content[userId] is List<dynamic> &&
+          accountData["m.direct"].content[userId].length > 0 &&
+          roomList.getRoomById(accountData["m.direct"].content[userId][0]) !=
+              null
+      ? accountData["m.direct"].content[userId][0]
+      : null;
 
   /// Checks the supported versions of the Matrix protocol and the supported
   /// login types. Returns false if the server is not compatible with the

lib/src/RoomList.dart

@@ -78,6 +78,13 @@ class RoomList {
     return null;
   }
 
+  Room getRoomById(String id) {
+    for (int j = 0; j < rooms.length; j++) {
+      if (rooms[j].id == id) return rooms[j];
+    }
+    return null;
+  }
+
   void _handleRoomUpdate(RoomUpdate chatUpdate) {
     // Update the chat list item.
     // Search the room in the rooms