fix: current prayer time 0:0 if next prayer fajr

[Moanrisy]

Bug: remaining time before next prayer is showing 0:0 if current prayer is isya

The usual next_prayer - current_time not gonna work
Because fajr time value is less than current time (after isya)

[azzamsa]

Thanks for finding all the bugs and all your awesome PRs! ❤️

I use this simpler approach instead.

        // Special case if the next prayer time is on the following day
        if self.next() == Prayer::FajrTomorrow {
            // Current time is after midnight
            if now.time() < self.fajr_tomorrow.time() {
                now += Duration::days(1);
            }
        }