Panicked at duration_round by zero

[ARBaart]

Hi, I ran into the following panic error in my Rust project using the duration_round method of chrono. The error is

panicked at 'attempt to calculate the remainder with a divisor of zero', /root/.cargo/registry/src/github.com-(...)/chrono-0.4.19/src/round.rs:161:30"

In the current master I think this corresponds to the following line:

chrono/src/round.rs

Line 188 in ea6412b

let delta_down = stamp % span;

It seems like duration_round doesn't check if the amount it is rounded by is zero, because the remainder operation (%) panics when used with zero as rhs. While rounding by zero doesn't make a lot of sense, the expected behaviour in the limit from higher values should probably be to just return the original value, unrounded.

Using Rust 1.56.0 and chrono 0.4.19

[djc]

Would you be able to submit a PR? I notice you're already working on a fix.

[ARBaart]

Would you be able to submit a PR? I notice you're already working on a fix.

Yes, see #659