Don't exit immediately if DBus isn't running

I am trying to run Dolphin on a minimal FreeBSD CHERI-RISC-V QEMU
instance and I haven't got DBus running. Without this change, KDBusService
causes dolphin to exit immediately since the default behaviour is to
exit if it can't connect to DBus.
1 job for master in 4 minutes and 28 seconds (queued for 268 minutes and 12 seconds)