Bugfix: matInvert returned an extra column of zeroes.
Bugfix: matInvert returned an extra column of zeroes.

This didn't matter in the places I called it because the result was
promptly multiplied by some other matrix of the correct size, and matrix
product was silently trimming off the excess column.

GaloisInc/ivory-tower-stm32,GaloisInc/ivory-tower-stm32,GaloisInc/ivory-tower-stm32