Silencing an exception from a task continuation requires accessing
`task.Exception` in any way, which was not done previously if
`logOnError` was false.
To resolve without having to worry whether the compiler will optimise
away a useless access or now, just always log, but switch the logging
level. The unimportant errors will be logged as debug and therefore
essentially silenced on release builds (but could still be potentially
useful in debugging).
