Variable FIXED_TIME_ON_tm_mday is not initialized on first check for time drift

[avnc]

Variable FIXED_TIME_ON_tm_mday is not initialized on first check for time drift. This causes an exception and keeps the clock from running past 12:01:30am.

[avnc]

Testing a fix for this now, simple (init variable when starting) but want to make sure works. If it does will submit PR.