Return nil from log* regardless of mode

The differing (and undocumented) return values from log* depending on *force* or implementation can have undesired effects on client code.  One could argue that the client code should guard against the return value of the log functions.  However, having the return value of log* be consistent will allow for more performant and cleaner code.

Signed-off-by: Chris Hapgood <cch1@hapgoods.com>