Warps as negative BPMs

Warps originated in `.sm` files as a glitch exploit using negative BPMs. These should be supported to maintain backwards compatibility, as a lot of popular `.sm` files used and abused this mechanic.

However, it seems `.dwi` files also had the same capability. Here is a [`.dwi` file](https://zenius-i-vanisher.com/simfiles/Hiryuu%27s%20Simfiles/V%5E3%20%28Hello%20World%29/V%5E3%20%28Hello%20World%29.dwi) and its counterpart [`.sm` file](https://zenius-i-vanisher.com/simfiles/Hiryuu%27s%20Simfiles/V%5E3%20%28Hello%20World%29/V%5E3%20%28Hello%20World%29.sm), both of which use negative BPM and stop values.

Investigation needs to be done to determine if the functionality was the same in the original Dance With Intensity simulator. Additionally, other file formats need similar investigation, such as `.msd` with the original DDR'99 simulator.