Use the same variable to check and extract LFS object id

It is easier to maintain when the same variable is used for both check
and extraction of LFS object id.

Change-Id: I5406f9bc4a085aa164c4565a9667ad2925105190
Signed-off-by: Jacek Centkowski <geminica.programs@gmail.com>

org.eclipse.jgit.lfs.server/src/org/eclipse/jgit/lfs/server/fs/FileLfsServlet.java

@@ -128,13 +128,14 @@ public class FileLfsServlet extends HttpServlet {
 	private AnyLongObjectId getObjectToTransfer(HttpServletRequest req,
 			HttpServletResponse rsp) throws IOException {
 		String info = req.getPathInfo();
-		if (info.length() != 1 + Constants.LONG_OBJECT_ID_STRING_LENGTH) {
+		int length = 1 + Constants.LONG_OBJECT_ID_STRING_LENGTH;
+		if (info.length() != length) {
 			sendError(rsp, HttpStatus.SC_UNPROCESSABLE_ENTITY, MessageFormat
 					.format(LfsServerText.get().invalidPathInfo, info));
 			return null;
 		}
 		try {
-			return LongObjectId.fromString(info.substring(1, 65));
+			return LongObjectId.fromString(info.substring(1, length));
 		} catch (InvalidLongObjectIdException e) {
 			sendError(rsp, HttpStatus.SC_UNPROCESSABLE_ENTITY, e.getMessage());
 			return null;