Always synchronize in Stepper::set_position

Marlin/stepper.cpp

  * derive the current XYZ position later on.
  */
 void Stepper::set_position(const long& x, const long& y, const long& z, const long& e) {
+
+  synchronize(); // Bad to set stepper counts in the middle of a move
+
   CRITICAL_SECTION_START;
 
   #if ENABLED(COREXY)