ATK: ATK/ATKMatrix: save path before freeing kernel

David Granstrom's patch:

I found the commit[1] which changes the implementation of freeMsg() in Buffer.sc
I have attached a patch with a solution for free() in ATKMatrix.sc…

[1] https://github.com/supercollider/supercollider/commit/7f29d322cf96e47cbad75eefcd195007f0ee4f92

Signed-off-by: Joseph Anderson <josephlloydanderson@mac.com>
Merge branch 'master' of https://github.com/supercollider/sc3-plugins