[PATCH] ref-filter: initialize empty name or email fields

[Mischa POSLAWSKY <git@shiar.nl>]

Formatting $(taggername) on headerless tags such as v0.99 in Git
causes a SIGABRT with error "munmap_chunk(): invalid pointer",
because of an oversight in commit f0062d3b74 (ref-filter: free
item->value and item->value->s, 2018-10-19).

Signed-off-by: Mischa POSLAWSKY <git@shiar.nl>
---
If I understand correctly, such tags cannot be produced normally anymore.
Therefore I'm unsure how to make tests, and if that is even warranted.

 ref-filter.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/ref-filter.c b/ref-filter.c
index f27cfc8c3e..7338cfc671 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -1028,7 +1028,7 @@ static const char *copy_name(const char *buf)
 		if (!strncmp(cp, " <", 2))
 			return xmemdupz(buf, cp - buf);
 	}
-	return "";
+	return xstrdup("");
 }
 
 static const char *copy_email(const char *buf)
@@ -1036,10 +1036,10 @@ static const char *copy_email(const char *buf)
 	const char *email = strchr(buf, '<');
 	const char *eoemail;
 	if (!email)
-		return "";
+		return xstrdup("");
 	eoemail = strchr(email, '>');
 	if (!eoemail)
-		return "";
+		return xstrdup("");
 	return xmemdupz(email, eoemail + 1 - email);
 }
 
-- 
2.23.0