monitor detection seems to be unreliable

[bstreiff]

I have two Dell U2412M monitors and a Dell E2417H.

Sometimes when running swmon list I get all three (reported via both winapi and nvapi):

 No.   Backend   Display ID                Manufacturer ID   Model Name
 0     winapi    Generic PnP Monitor       ?                 U2412M
 1     winapi    Generic PnP Monitor       ?                 U2412M
 2     winapi    Generic PnP Monitor       ?                 E2417H
 3     nvapi     GA106-A/2147881090:Lvds   DEL               DELL U2412M
 4     nvapi     GA106-A/2147881088:Lvds   DEL               DELL U2412M
 5     nvapi     GA106-A/2147881094:Lvds   DEL               DELL E2417H

However if I run swmon list over and over, sometimes monitors are missing.

 No.   Backend   Display ID                Manufacturer ID   Model Name
 1     winapi    Generic PnP Monitor       ?                 U2412M
 2     winapi    Generic PnP Monitor       ?                 E2417H
 5     nvapi     GA106-A/2147881094:Lvds   DEL               DELL E2417H

For whatever reason the effect seems to be particularly bad in swmon-gui: I don't think I've seen all six entries show up.

[cr1901]

Low hanging fruit for me to try if I can duplicate locally:

• is_ok is probably not the right thing to do here, and I should actually handle error conditions (if even possible since ddc-hi uses anyhow and thus might not be practical to downcast all possible errors that can show up).

• If enumeration errors out, it doesn't show up in the list of available monitors. Is it possible to make a combo box w/ some entries greyed out?