Fix: commands with Axis in their arguments were not validated properly (#9943)

When you don't type an Enum, it is a signed value. To validate
if an Axis is valid, it is checked to be lower than AXIS_END. Which
is the case for any value below 0.

src/direction_type.h

@@ -120,7 +120,7 @@ DECLARE_POSTFIX_INCREMENT(DiagDirDiff)
  * (and south-east edge). The Y axis must be so the one which goes
  * align the north-east edge (and south-west) edge.
  */
-enum Axis {
+enum Axis : byte {
 	AXIS_X = 0,          ///< The X axis
 	AXIS_Y = 1,          ///< The y axis
 	AXIS_END,            ///< Used for iterations