Clarify time epsilon

[ThomasBrierley]

t*60|0 is often used in dweets to acquire the current frame, however t/60 and t*60 have asymmetric rounding error, and for some frames this causes t*60|0 to evaluate to the previous frame.

The existing condition was intended to explicitly check for this mismatch and compensate by adding a small number to t. The condition is broken and actually adds 1e-6 to every non-zero frame, however this is not a problem until the 2147483648th frame, which is good enough.

We shouldn't fix the condition because some dweets are sensitive to t and will have come to depend on this detail. But we can re-write the code to reflect this choice, and comment it for preservation.

[ThomasBrierley]

This is purely for legibility and comprehension, it does not affect the running of dweets in any way.