[infer] Fix ObjectWalk leak in PackWriter.preparePack()

Change-Id: I5d2455404e507faa717e9d916e9b6cd80aa91473
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackWriter.java

@@ -745,15 +745,16 @@ public class PackWriter implements AutoCloseable {
 			@NonNull Set<? extends ObjectId> want,
 			@NonNull Set<? extends ObjectId> have,
 			@NonNull Set<? extends ObjectId> shallow) throws IOException {
-		ObjectWalk ow;
-		if (shallowPack) {
-			ow = new DepthWalk.ObjectWalk(reader, depth - 1);
-		} else {
-			ow = new ObjectWalk(reader);
-		}
+		try (ObjectWalk ow = getObjectWalk()) {
 			ow.assumeShallow(shallow);
 			preparePack(countingMonitor, ow, want, have);
 		}
+	}
+
+	private ObjectWalk getObjectWalk() {
+		return shallowPack ? new DepthWalk.ObjectWalk(reader, depth - 1)
+				: new ObjectWalk(reader);
+	}
 
 	/**
 	 * Prepare the list of objects to be written to the pack stream.