fix check for remote server

As remote server is empty instead null when not available, the check was also true when no remote server was in use.

Signed-off-by: Marcel Hibbe <dev@mhibbe.de>

app/src/main/java/com/nextcloud/talk/chat/ChatActivity.kt

@@ -2514,7 +2514,7 @@ class ChatActivity :
             return
         }
 
-        if (currentConversation!!.remoteServer != null) {
+        if (currentConversation!!.remoteServer?.isNotEmpty() == true) {
             val apiVersion = ApiUtils.getSignalingApiVersion(conversationUser!!, intArrayOf(ApiUtils.API_V3, 2, 1))
             ncApi.getSignalingSettings(
                 credentials,