Program exits on F5 trying to parse wrong flags

[paoloose]

When restarting with F5, this for loop will try to parse_time all flags other than -p

https://github.com/tsoding/sowon/blob/eb3a37c4dbd996e3c077a840b18852d4af25367f/main.c#L238-L253

So when running with -e or clock mode and hit F5, the application will close with '-e' is not a number and 'clock' is not a number respectively.

I will make a PR :)