mailmap: debug: fix malformed fprintf() format conversion specification

Resolve segmentation fault due to size_t variable being consumed by
'%s'.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: sunshineco

mailmap.c

@@ -337,7 +337,7 @@ int map_user(struct string_list *map,
 				*name = mi->name;
 				*namelen = strlen(*name);
 		}
-		debug_mm("map_user:  to '%.*s' <.*%s>\n", *namelen, *name,
+		debug_mm("map_user:  to '%.*s' <%.*s>\n", *namelen, *name,
 				 *emaillen, *email);
 		return 1;
 	}