Fix: Close the "preserved" PackDirectory

This has been missing since the feature was first added in commit
6167641834e28f8ad322f8fde60866b339bfb7fe.

It's possible we could be more aggressive and close soon after
attempting to get an object from the preserved packs, but for concurrent
misses that might cause thrashing. More likely it would be safe to
attempt closing after successfully restoring a preserved pack. A follow
up change should attempt that.

Change-Id: I87d61007bcc3d03fc86bd18465ca66a2e6f697a1

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

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
index 9f21481..3a6de4e 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/file/ObjectDirectory.java
@@ -200,6 +200,7 @@ public void close() {
 		loose.close();
 
 		packed.close();
+		preserved.close();
 
 		// Fully close all loaded alternates and clear the alternate list.
 		AlternateHandle[] alt = alternates.get();