Fix plan_arc clockwise (G2)

Fix #9482

Marlin/src/gcode/motion/G2_G3.cpp

     angular_travel = RADIANS(360);
 
   const float flat_mm = radius * angular_travel,
-              mm_of_travel = linear_travel ? HYPOT(flat_mm, linear_travel) : flat_mm;
+              mm_of_travel = linear_travel ? HYPOT(flat_mm, linear_travel) : FABS(flat_mm);
   if (mm_of_travel < 0.001) return;
 
   uint16_t segments = FLOOR(mm_of_travel / (MM_PER_ARC_SEGMENT));