config: Avoid buffer overflow

Signed-off-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
(cherry picked from commit 1af10fcdb3)

src/config.c

@@ -210,6 +210,7 @@ static struct ssh_config_match_keyword_table_s ssh_config_match_keyword_table[]
     { "originalhost", MATCH_ORIGINALHOST },
     { "user", MATCH_USER },
     { "localuser", MATCH_LOCALUSER },
+    { NULL, MATCH_UNKNOWN },
 };
 
 static int ssh_config_parse_line(ssh_session session, const char *line,