Check condition for writing c3d file

[beebuzz002]

I feel that this method is a smoother alternative. This will be able to perform the check without any errors caused and would not rely on other functions to smooth the value out.

---

This change is 

[beebuzz002]

Hi @pariterre, The goal is to compare integer points only, since all 4 values (number of analog frames, number of point frames, analog frame rate and point frame rate) are expected to be integers. The use of multiplication also ensures that the resulting values are integers.