G28/30 bug fix. Block '$$' during cycle. SO2 defaults.

- A G28/30 bug would cause it to move to machine coordinate [0,0,0] if
no axis words were sent. It was a typo in the new g-code parser. Fixed
and slightly re-written to be more consistent with the program flow.

- Updated the ShapeOko2 defaults based on testing on the real machine.
A little conservative, but it might change again after some more
testing.

- Now blocks ‘$$’ command during a motion, because the printout takes
too long and can starve the segment buffer.

gcode.c

@@ -610,11 +610,13 @@ uint8_t gc_execute_line(char *line)
         case NON_MODAL_GO_HOME_0: 
           // [G28 Errors]: Cutter compensation is enabled. 
           // Retreive G28 go-home position data (in machine coordinates) from EEPROM
+          if (!axis_words) { axis_command = AXIS_COMMAND_NONE; } // Set to none if no intermediate motion.
           if (!settings_read_coord_data(SETTING_INDEX_G28,parameter_data)) { FAIL(STATUS_SETTING_READ_FAIL); }
           break;
         case NON_MODAL_GO_HOME_1:
           // [G30 Errors]: Cutter compensation is enabled. 
           // Retreive G30 go-home position data (in machine coordinates) from EEPROM
+          if (!axis_words) { axis_command = AXIS_COMMAND_NONE; } // Set to none if no intermediate motion.
           if (!settings_read_coord_data(SETTING_INDEX_G30,parameter_data)) { FAIL(STATUS_SETTING_READ_FAIL); }
           break;
         case NON_MODAL_SET_HOME_0: case NON_MODAL_SET_HOME_1: