device-manager: improve logging about non-existing data

device-manager: improve logging about non-existing data

Previously a missing key would cause this kind of log output:

D: [pulseaudio] module-device-manager.c: Database contains invalid data for key: sink:auto_null (probably pre-v1.0 data)
D: [pulseaudio] module-device-manager.c: Attempting to load legacy (pre-v1.0) data for key: sink:auto_null
D: [pulseaudio] module-device-manager.c: Size does not match.
D: [pulseaudio] module-device-manager.c: Unable to load legacy (pre-v1.0) data for key: sink:auto_null. Ignoring.

That is now replaced with

D: [pulseaudio] module-device-manager.c: Database contains no data for key: sink:auto_null