Correct some log messages.
Add some more info log output to show when we try to download images.
SubjectAdder.downloadMissingImages(): Don't try if there is no network.

We already ignore the exception in the caller, because it is normal,
though we didn't actually throw the exception.
The lack of a check here might have caused us to download missing images,
though not new images, while not on wifi even while the wifi-only
setting was on.