Use try-with-resources to close walks in ArchiveCommand

Change-Id: I77120d77a12f1bab5c918a23b0e3eac90e320b2b
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/api/ArchiveCommand.java

@@ -365,13 +365,11 @@ public class ArchiveCommand extends GitCommand<OutputStream> {
 
 	private <T extends Closeable> OutputStream writeArchive(Format<T> fmt) {
 		final String pfx = prefix == null ? "" : prefix; //$NON-NLS-1$
-		final TreeWalk walk = new TreeWalk(repo);
-		try {
+		try (final TreeWalk walk = new TreeWalk(repo)) {
 			final T outa = fmt.createArchiveOutputStream(out, formatOptions);
-			try {
+			try (final RevWalk rw = new RevWalk(walk.getObjectReader())) {
 				final MutableObjectId idBuf = new MutableObjectId();
 				final ObjectReader reader = walk.getObjectReader();
-				final RevWalk rw = new RevWalk(walk.getObjectReader());
 
 				walk.reset(rw.parseTree(tree));
 				if (!paths.isEmpty())
@@ -405,8 +403,6 @@ public class ArchiveCommand extends GitCommand<OutputStream> {
 			// TODO(jrn): Throw finer-grained errors.
 			throw new JGitInternalException(
 					JGitText.get().exceptionCaughtDuringExecutionOfArchiveCommand, e);
-		} finally {
-			walk.release();
 		}
 	}