use strbuf_addch for adding single characters

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/pathspec.c b/pathspec.c
index 8043099..89f2c8f 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -338,7 +338,7 @@
 		if (!(magic & m->bit))
 			continue;
 		if (sb.len)
-			strbuf_addstr(&sb, " ");
+			strbuf_addch(&sb, ' ');
 		if (short_magic & m->bit)
 			strbuf_addf(&sb, "'%c'", m->mnemonic);
 		else