LfsProtocolServlet: Always set the Content-Type header on response

If the Content-Type is not set on error responses, the git-lfs client
does not read the body which contains the error message, and instead
just displays a generic error message.

Also set the charset on the Content-Type header.

Change-Id: I88e6f07f20b622a670e7c5063145dffb8b630aee
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

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

@@ -83,7 +83,8 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 
 	private static final long serialVersionUID = 1L;
 
-	private static final String CONTENTTYPE_VND_GIT_LFS_JSON = "application/vnd.git-lfs+json"; //$NON-NLS-1$
+	private static final String CONTENTTYPE_VND_GIT_LFS_JSON =
+			"application/vnd.git-lfs+json; charset=utf-8"; //$NON-NLS-1$
 
 	private Gson gson = createGson();
 
@@ -143,6 +144,7 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 		LfsRequest request = gson.fromJson(r, LfsRequest.class);
 		String path = req.getPathInfo();
 
+		res.setContentType(CONTENTTYPE_VND_GIT_LFS_JSON);
 		LargeFileRepository repo = null;
 		try {
 			repo = getLargeFileRepository(request, path);
@@ -150,7 +152,6 @@ public abstract class LfsProtocolServlet extends HttpServlet {
 				res.setStatus(SC_SERVICE_UNAVAILABLE);
 			} else {
 				res.setStatus(SC_OK);
-				res.setContentType(CONTENTTYPE_VND_GIT_LFS_JSON);
 				TransferHandler handler = TransferHandler
 						.forOperation(request.operation, repo, request.objects);
 				gson.toJson(handler.process(), w);