pack: move prepare_packed_git_run_once to object store

Each repository's object store can be initialized independently, so
they must not share a run_once variable.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

object-store.h

@@ -98,6 +98,12 @@ struct raw_object_store {
 	struct packed_git *packed_git;
 	/* A most-recently-used ordered version of the packed_git list. */
 	struct list_head packed_git_mru;
+
+	/*
+	 * Whether packed_git has already been populated with this repository's
+	 * packs.
+	 */
+	unsigned packed_git_initialized : 1;
 };
 
 struct raw_object_store *raw_object_store_new(void);