LfsProtocolServlet: Always include message in error response

If the message is not sent, the client shows:

  Unable to parse HTTP response for POST http://admin@localhost:8080/test-project/info/lfs/objects/batch

Change-Id: I8b72d1aded2bcd41b7389676e2373034625a1379
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/LfsProtocolServlet.java

@@ -149,7 +149,8 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 		try {
 			repo = getLargeFileRepository(request, path);
 			if (repo == null) {
-				res.setStatus(SC_SERVICE_UNAVAILABLE);
+				sendError(res, w, SC_SERVICE_UNAVAILABLE,
+						"LFS is not available"); //$NON-NLS-1$
 			} else {
 				res.setStatus(SC_OK);
 				TransferHandler handler = TransferHandler