[FluidNC PR#1586] Fix invalid_arc routine to check for full rotations in G2/G3 arc commands

Simple fixes to account for the fact that if G2/G3 commands include Pn with n > 1, arcs perform at least one full rotation in the working plane before arriving at the final position.

Before, the invalid_arc routine did not contemplate this but rather calculated the min/max positions along the commanded path by considering a partial arc between the current and desired position.

With these changes, the routine correctly contemplates the case where n > 1 and calculates the min/max coordinates in the working plane along the commanded path correctly.