[fizzed#15] Writing data on closed socket causes unnecessary exceptio…

…n in Netty

.gitignore

@@ -3,4 +3,4 @@ target/
 .classpath
 .project
 .settings/
-
+.idea/

src/main/java/com/cloudhopper/smpp/impl/DefaultSmppSession.java

@@ -516,6 +516,11 @@ public WindowFuture<Integer,PduRequest,PduResponse> sendRequestPdu(PduRequest pd
             }
         }
 
+        if (!this.channel.isOpen()) {
+            logger.info("Channel closed.");
+            return future;
+        }
+
         // we need to log the PDU after encoding since some things only happen
         // during the encoding process such as looking up the result message
         if (configuration.getLoggingOptions().isLogPduEnabled()) {