Ensure DirectoryStream is closed promptly

From the javadoc for Files.list:

"The returned stream encapsulates a DirectoryStream. If timely disposal
of file system resources is required, the try-with-resources construct
should be used to ensure that the stream's close method is invoked
after the stream operations are completed."

This is the only call to Files#newDirectoryStream that is not already in
a try-with-resources.

Change-Id: I91e6c56b5d74e8435457ad6ed9e6b4b24d2aa14e
(cherry picked from commit 1c16ea4601)

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/GC.java

@@ -966,19 +966,19 @@ public class GC {
 		Path packDir = Paths.get(repo.getObjectsDirectory().getAbsolutePath(),
 				"pack"); //$NON-NLS-1$
 		Instant threshold = Instant.now().minus(1, ChronoUnit.DAYS);
-		try {
-			Files.newDirectoryStream(packDir, "gc_*_tmp") //$NON-NLS-1$
-					.forEach(t -> {
-						try {
-							Instant lastModified = Files.getLastModifiedTime(t)
-									.toInstant();
-							if (lastModified.isBefore(threshold)) {
-								Files.deleteIfExists(t);
-							}
-						} catch (IOException e) {
-							LOG.error(e.getMessage(), e);
-						}
-					});
+		try (DirectoryStream<Path> stream =
+				Files.newDirectoryStream(packDir, "gc_*_tmp")) { //$NON-NLS-1$
+			stream.forEach(t -> {
+				try {
+					Instant lastModified = Files.getLastModifiedTime(t)
+							.toInstant();
+					if (lastModified.isBefore(threshold)) {
+						Files.deleteIfExists(t);
+					}
+				} catch (IOException e) {
+					LOG.error(e.getMessage(), e);
+				}
+			});
 		} catch (IOException e) {
 			LOG.error(e.getMessage(), e);
 		}