Add temp buffer allocation and don't set config slots unless config allocated successfully

o The alloc routines didn't actually allocate any space for the temp
  buffer that is used in the FFT routines.  Allocate space for the
  temp buffer.  Someone needs to check that the allocated space is
  correct.

o Various slots of the config were set before testing to see if the
  allocation of the config succeeded.  Move the code after the check.