repo-settings: prepare_repo_settings only in git repos

Check whether git directory exists before adding any repo settings. If it
does not exist, BUG with the message that one cannot add settings for an
uninitialized repository. If it does exist, proceed with adding repo
settings.

Signed-off-by: Lessley Dennington <lessleydennington@gmail.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

repo-settings.c

@@ -17,6 +17,9 @@ void prepare_repo_settings(struct repository *r)
 	char *strval;
 	int manyfiles;
 
+	if (!r->gitdir)
+		BUG("Cannot add settings for uninitialized repository");
+
 	if (r->settings.initialized++)
 		return;