Bugs:
* ffd animation was ignoring last frame. Lua has 1-based arrays, so last frame is `frames[#frames]`, not `frames[#frames - 1]`
* nil exception when accessing array lenght after it's confirmed nil. First we check if `not vertices` and in next statement we're trying to check for it's length, which causes exception. This code is logically equivalent to code before but avoids checking potentially nil array for length.
