Return the documented value from DirCacheCheckout.checkout

Change-Id: I34d773b18e6a1ee05774d7b9471f9915c48aa63e
Signed-off-by: Robin Rosenberg <robin.rosenberg@dewire.com>

org.eclipse.jgit/src/org/eclipse/jgit/dircache/DirCacheCheckout.java

@@ -352,7 +352,7 @@ public class DirCacheCheckout {
 			throw new IndexWriteException();
 		}
 
-		return toBeDeleted == null;
+		return toBeDeleted.size() == 0;
 	}
 
 	private static boolean isSamePrefix(String a, String b) {