This post process step introduced new attributes into `aiSkeletonBone`. Said attributes are only defined with the process enabled, i.e. when the `ASSIMP_BUILD_NO_ARMATUREPOPULATE_PROCESS` macro has not been defined.
Some code, however, accessed the variables unconditionally, leading to build failures if `ASSIMP_BUILD_NO_ARMATUREPOPULATE_PROCESS` was defined.
This commit adds the missing checks.
793284a766