Make sure the "avoid crossing perimeters" class is resetted

at the start of G-code export.

src/libslic3r/GCode.cpp

@@ -1012,6 +1012,7 @@ void GCode::_do_export(Print &print, FILE *file)
     _write(file, this->preamble());
 
     // Initialize a motion planner for object-to-object travel moves.
+    m_avoid_crossing_perimeters.reset();
     if (print.config().avoid_crossing_perimeters.value) {
         m_avoid_crossing_perimeters.init_external_mp(print);
         print.throw_if_canceled();

src/libslic3r/GCode.hpp

@@ -45,6 +45,7 @@ public:
     AvoidCrossingPerimeters() : use_external_mp(false), use_external_mp_once(false), disable_once(true) {}
     ~AvoidCrossingPerimeters() {}
 
+    void reset() { m_external_mp.reset(); m_layer_mp.reset(); }
 	void init_external_mp(const Print &print);
     void init_layer_mp(const ExPolygons &islands) { m_layer_mp = Slic3r::make_unique<MotionPlanner>(islands); }