[Modify] Polish it

websocket-sharp/WebSocket.cs

@@ -310,7 +310,6 @@ namespace WebSocketSharp
       }
 
       set {
-        lock (_forState) {
         string msg;
         if (!checkIfAvailable (true, false, true, false, false, true, out msg)) {
           _logger.Error (msg);
@@ -319,6 +318,14 @@ namespace WebSocketSharp
           return;
         }
 
+        lock (_forState) {
+          if (!checkIfAvailable (true, false, false, true, out msg)) {
+            _logger.Error (msg);
+            error ("An error has occurred in setting the compression.", null);
+
+            return;
+          }
+
           _compression = value;
         }
       }