Check non-flushed packs for existence of object

Change-Id: Id466909d70ec6f828c904692139891dec880305e
Signed-off-by: Zhen Chen <czhen@google.com>

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsInserter.java

@@ -615,6 +615,12 @@ public class DfsInserter extends ObjectInserter {
 			}
 		}
 
+		@Override
+		public boolean has(AnyObjectId objectId) throws IOException {
+			return (objectMap != null && objectMap.contains(objectId))
+					|| ctx.has(objectId);
+		}
+
 		@Override
 		public Set<ObjectId> getShallowCommits() throws IOException {
 			return ctx.getShallowCommits();