In a6840296, a refactor to the `config` class was introduced.
The change included an internal wrapper for `reactor.callLater`, for lazy
import, but didn't wrap it correctly and therefor, no args/kwargs were
passed to the wrapped method.
Furthermore, the exception was silently ignored.
This caused changes to be ignored and not applied, including
`preferencesmanager._on_config_value_change` callback.
Closes: https://github.com/deluge-torrent/deluge/pull/372
f8f997a6eb