imap,pop3: Properly terminate logout tab.

Fixes Fatal: master: service(imap): child killed with signal 11

Broken in e0a42ca and
1ecc087

src/imap/imap-client.c

@@ -266,6 +266,7 @@ const char *client_stats(struct client *client)
 		{ '\0', dec2str(client->trashed_count), "trashed" },
 		{ '\0', dec2str(client->autoexpunged_count), "autoexpunged" },
 		{ '\0', dec2str(client->append_count), "appended" },
+		{ '\0', NULL, NULL }
 	};
 	const struct var_expand_table *user_tab =
 		mail_user_var_expand_table(client->user);

src/pop3/pop3-client.c

@@ -539,6 +539,7 @@ static const char *client_stats(struct client *client)
 		{ '\0', client->session_id, "session" },
 		{ 'd', !client->delete_success ? "0" :
 		       dec2str(client->deleted_size), "deleted_bytes" },
+		{ '\0', NULL, NULL }
 	};
 	const struct var_expand_table *user_tab =
 		mail_user_var_expand_table(client->user);