phonefsod-fso: delay showing PIN dialog on device status handler

This fixes race condition from #2094.

phoneuid just appeared on the bus, but modem wasn't ready yet.
It became ready very soon, so status handler tried to show PIN dialog,
but phoneuid wasn't ready yet (as in #1478), so call failed, leaving
user without PIN dialog at all.

Signed-off-by: Sebastian Krzyszkowiak <dos@dosowisko.net>