notes.c: fix a segfault in notes_display_config()

If notes.displayRef is configured with no value[1], control should be
returned to the caller when notes.c:notes_display_config() checks if 'v'
is NULL. Otherwise, both git log --notes and git diff-tree --notes will
subsequently segfault when refs.h:has_glob_specials() calls strpbrk()
with a NULL first argument.

[1] Examples:
.git/config:
[notes]
	displayRef
$ git -c notes.displayRef [...]

Signed-off-by: Nate Avers <nate@roosteregg.cc>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/notes.c b/notes.c
index 03e7d0cd2d..928dde8b34 100644
--- a/notes.c
+++ b/notes.c
@@ -967,7 +967,7 @@ static int notes_display_config(const char *k, const char *v, void *cb)
 
 	if (*load_refs && !strcmp(k, "notes.displayref")) {
 		if (!v)
-			config_error_nonbool(k);
+			return config_error_nonbool(k);
 		string_list_add_refs_by_glob(&display_notes_refs, v);
 	}