Check for sending a close frame

TooTallNate#579

Author: marci4

pom.xml

@@ -7,6 +7,9 @@
   <name>Java-WebSocket</name>
   <description>A barebones WebSocket client and server implementation written 100% in Java</description>
   <url>https://github.com/TooTallNate/Java-WebSocket</url>
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
   <licenses>
     <license>
       <name>MIT License</name>

src/main/java/org/java_websocket/WebSocketImpl.java

@@ -424,11 +424,13 @@ public void close( int code, String message, boolean remote ) {
 								wsl.onWebsocketError( this, e );
 							}
 						}
-						CloseFrame closeFrame = new CloseFrame();
-						closeFrame.setReason( message );
-						closeFrame.setCode( code );
-						closeFrame.isValid();
-						sendFrame( closeFrame );
+						if (isOpen()) {
+							CloseFrame closeFrame = new CloseFrame();
+							closeFrame.setReason( message );
+							closeFrame.setCode( code );
+							closeFrame.isValid();
+							sendFrame( closeFrame );
+						}
 					} catch ( InvalidDataException e ) {
 						wsl.onWebsocketError( this, e );
 						flushAndClose( CloseFrame.ABNORMAL_CLOSE, "generated frame is invalid", false );