pam_systemd_home: make sure we handle RefUnit() returning HomeBusy pr…

…operly

RefUnit() only succeeds it a home dir is fully up. We already dealt with
it not being up at all, but let's also cover the case where it is
currently busy with changing state, and in that case fall back to
RefUnrestricted(), with the usual implications.

This has the effect that two subsequent ssh logins one-after-the-other
will work correctly.

src/home/pam_systemd_home.c

@@ -621,7 +621,7 @@ static int acquire_home(
 
                 r = sd_bus_call(bus, m, HOME_SLOW_BUS_CALL_TIMEOUT_USEC, &error, &reply);
                 if (r < 0) {
-                        if (sd_bus_error_has_name(&error, BUS_ERROR_HOME_NOT_ACTIVE)) {
+                        if (sd_bus_error_has_names(&error, BUS_ERROR_HOME_NOT_ACTIVE, BUS_ERROR_HOME_BUSY)) {
                                 /* Only on RefHome(): We can't access the home directory currently, unless
                                  * it's unlocked with a password. Hence, let's try this again, this time with
                                  * authentication. */