Scanner: Open RevWalk in try-with-resource

Change-Id: Ieeec292c1346edbda2b26f021e75cbc1435bb9f9
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/reftree/Scanner.java

@@ -221,10 +221,11 @@ class Scanner {
 		return new SymbolicRef(ref.getName(), dst);
 	}
 
-	@SuppressWarnings("resource")
 	private static RevTree toTree(ObjectReader reader, AnyObjectId id)
 			throws IOException {
-		return new RevWalk(reader).parseTree(id);
+		try (RevWalk rw = new RevWalk(reader)) {
+			return rw.parseTree(id);
+		}
 	}
 
 	private static boolean curElementHasPeelSuffix(AbstractTreeIterator itr) {