The standard library has the implicit requirement that for
std::condition_variable::sleep_for() the duration must not cause an
overflow if added to the current time.
This commit will reduce the duration accordingly to fit into the
duration type.
This keeps the function consistent with sleep_until() and sleep_for()
which both can be interrupted.
This is relevant to allow an update via a "signal" without an "interval"
in a custom module.
Tamino Bauknecht