switch-on-port-available: checking the off profile when switching profile

switch-on-port-available: checking the off profile when switching profile

If the current active profile is off, it has no sinks and sources, and
if users plug a headset to the audio port, the profile including this
audio port becomes available and should be selected as active profile.

But with the current design, the profile_good_for_output() will return
false because the sources in off profile and target profile doesn't
match.

For example:
(Before users plug headset)
Profiles:
         HiFi (Speaker): Default (sinks: 1, sources: 1, priority: 8100, available: no)
         HiFi (Headphones): Default (sinks: 1, sources: 1, priority: 8200, available: no)
         off: Off (sinks: 0, sources: 0, priority: 0, available: yes)
Active Profile: off

(After users plug headset)
Profiles:
         HiFi (Speaker): Default (sinks: 1, sources: 1, priority: 8100, available: yes)
         HiFi (Headphones): Default (sinks: 1, sources: 1, priority: 8200, available: yes)
         off: Off (sinks: 0, sources: 0, priority: 0, available: yes)
Active Profile: off

Signed-off-by: Hui Wang <hui.wang@canonical.com>
Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/354>