Handle controller extrapolation flags
In magic_hit_myst.nif, there's NiKeyframeControllers containing keyframes with negative times (seriously?). This is not supported by OpenMW and as result the particle effect looks different (the emitters don't rotate). I think NifOgre::DefaultFunction::calculate needs to be adjusted to support this.
(RM-1871 from redmine: created on 2014-09-02 by scrawl ., , closed on 2015-06-30 by scrawl .)