Updated key to avoid collisions at time zero

[theo-rogers]

Using just fromMs as a key will end up in 0 being a key when time = 0. This is likely to cause a key collision.

[egorovsa]

Hi there! Thanks for your PR.
Could you please clarify what the keys collisions do you mean?
I see it if only you provide two timecodes with fromMs = 0 whereas this is a mistaken props.
So I can't see any cases where two timecodes have keys 0