Bug 1078243 - [Costcontrol] When the Starting day of the reset period is...

... 31th, the app does not calculated correctly the end of the reset period.
Can we extract `today.getDate() > monthDate` to a `isAfterFirstDayOfPeriod` variable. Morevoer, this implies `!isFirstDayOfPeriod` so it is enough to check `if (isAfterFirstDayOfPeriod) ...`