Coverage data shows that we didn't test calendar_spec_next_usec() and
associated functions at all.
The input samples so far were only used until the first NUL. We take advantage
of that by using the part until the second NUL as the starting timestamp,
retaining backwards compatibility for how the first part is used.
calendar_spec_from_string() already calls calendar_spec_normalize(), so
there is no point in calling it from the fuzzer. Once that's removed, there's
just one internal caller and it can be made static.
Zbigniew Jędrzejewski-Szmek
Yu Watanabe
Frantisek Sumsal