Invalid command line inputs need to be caught and exec halted right away

[bskinn]

Annoying for a user to wait for a while, e.g., for a CUBE to be fully pulled into memory, only to have execution halt due to bad input

• Negative 'min' in absolute thresholding mode

Probably there are others. Basically, checks for every invalid commandline value need to be promoted to happen before any loading from disk happens!