Merge branch 'bc/fetch-pack-clear-alternate-shallow'

"git fetch" over protocol v2 that needs to make a second connection
to backfill tags did not clear a variable that holds shallow
repository information correctly, leading to an access of freed
piece of memory.

* bc/fetch-pack-clear-alternate-shallow:
  fetch-pack: clear alternate shallow in one more place
  fetch-pack: clear alternate shallow when complete

fetch-pack.c

@@ -1290,6 +1290,8 @@ static void receive_shallow_info(struct fetch_pack_args *args,
 		setup_alternate_shallow(&shallow_lock, &alternate_shallow_file,
 					NULL);
 		args->deepen = 1;
+	} else {
+		alternate_shallow_file = NULL;
 	}
 }
@@ -1514,6 +1516,7 @@ static void update_shallow(struct fetch_pack_args *args,
 			rollback_lock_file(&shallow_lock);
 		} else
 			commit_lock_file(&shallow_lock);
+		alternate_shallow_file = NULL;
 		return;
 	}
@@ -1537,6 +1540,7 @@ static void update_shallow(struct fetch_pack_args *args,
 						&alternate_shallow_file,
 						&extra);
 			commit_lock_file(&shallow_lock);
+			alternate_shallow_file = NULL;
 		}
 		oid_array_clear(&extra);
 		return;
@@ -1576,6 +1580,7 @@ static void update_shallow(struct fetch_pack_args *args,
 		commit_lock_file(&shallow_lock);
 		oid_array_clear(&extra);
 		oid_array_clear(&ref);
+		alternate_shallow_file = NULL;
 		return;
 	}