Provide default case for switches

[jeremypw]

Silences some compile warnings. Assumes missed cases do not need handling.

[danirabbit]

for the appstream icons, it might be better to explicitly include AppStream.IconKind.UNKNOWN in case a new IconKind is introduced we probably would want this to warn again

I wonder if it would be better to do the same with Pk.ProgressType so we're at least documenting the status' we're ignoring and making sure we know it's intentional: https://valadoc.org/packagekit-glib2/Pk.ProgressType.html

[jeremypw]

I added a warning for unknown AppStream.IconKind but I have held off from doing the same for Pk.ProgressType as that resulted in the terminal getting spammed with lots of warnings for each package updated.

[danirabbit]

@jeremypw in that case maybe we shouldn't touch the Pk.ProgressType since that sounds like maybe an issue that needs to be addressed and hiding the warning here just hides the issue instead of actually fixing it

In my previous comment I wasn't saying we needed to add a warning to the case handler, but that if the enum changed in future library versions, we would get a compiler warning again instead of using default where we wouldn't be alerted that new types were added to the enum

[jeremypw]

Sorry I misunderstood your original comment. Hope I have got it right now.

Changes made and approved by @tintou