Merge branch 'nd/repo-clear-keep-the-index'

the_repository->index is not a allocated piece of memory but
repo_clear() indiscriminately attempted to free(3) it, which has
been corrected.

* nd/repo-clear-keep-the-index:
  repository: fix free problem with repo_clear(the_repository)

Author: gitster

repository.c

@@ -238,7 +238,8 @@ void repo_clear(struct repository *repo)
 
 	if (repo->index) {
 		discard_index(repo->index);
-		FREE_AND_NULL(repo->index);
+		if (repo->index != &the_index)
+			FREE_AND_NULL(repo->index);
 	}
 }