Only compute StringData bytes once, close AsyncHttpClient#263

Author: Stephane Landelle

providers/netty/src/main/java/com/ning/http/client/providers/netty/NettyAsyncHttpProvider.java

@@ -779,8 +779,9 @@ else if (uri.getRawQuery() != null)
                     nettyRequest.setHeader(HttpHeaders.Names.CONTENT_LENGTH, String.valueOf(request.getByteData().length));
                     nettyRequest.setContent(ChannelBuffers.wrappedBuffer(request.getByteData()));
                 } else if (request.getStringData() != null) {
-                    nettyRequest.setHeader(HttpHeaders.Names.CONTENT_LENGTH, String.valueOf(request.getStringData().getBytes(bodyCharset).length));
-                    nettyRequest.setContent(ChannelBuffers.wrappedBuffer(request.getStringData().getBytes(bodyCharset)));
+                    byte[] bytes = request.getStringData().getBytes(bodyCharset);
+                    nettyRequest.setHeader(HttpHeaders.Names.CONTENT_LENGTH, String.valueOf(bytes.length));
+                    nettyRequest.setContent(ChannelBuffers.wrappedBuffer(bytes));
                 } else if (request.getStreamData() != null) {
                     int[] lengthWrapper = new int[1];
                     byte[] bytes = AsyncHttpProviderUtils.readFully(request.getStreamData(), lengthWrapper);