[Modify] Polish it

websocket-sharp/WebSocket.cs

@@ -3342,12 +3342,16 @@ namespace WebSocketSharp
       if (fileInfo == null)
         throw new ArgumentNullException ("fileInfo");
 
-      if (!fileInfo.Exists)
+      if (!fileInfo.Exists) {
-        throw new ArgumentException ("The file does not exist.", "fileInfo");
+        var msg = "The file does not exist.";
+        throw new ArgumentException (msg, "fileInfo");
+      }
 
       FileStream stream;
-      if (!fileInfo.TryOpenRead (out stream))
+      if (!fileInfo.TryOpenRead (out stream)) {
-        throw new ArgumentException ("The file could not be opened.", "fileInfo");
+        var msg = "The file could not be opened.";
+        throw new ArgumentException (msg, "fileInfo");
+      }
 
       sendAsync (Opcode.Binary, stream, completed);
     }