G-code parser G0/G1 bug fix.

- Although stated as invalid in the NIST g-code standard, most g-code
parsers, including linuxcnc, allow G0 and G1 to be commanded without
axis words present. For example, something like ‘G1 F100.0’ to preset
the motion mode and feed rate without a motion commanded. Older CNC
controllers actually required this for feed rate settings. This update
should now allow this type of behavior.