Fixed crash on reslicing after infill invalidation.

The crash was introduced with sorting the extrusions into islands.

src/libslic3r/Fill/Fill.cpp

@@ -408,12 +408,18 @@ static void insert_fills_into_islands(Layer &layer, uint32_t fill_region_id, uin
     }
 }
 
-// friend to Layer
+void Layer::clear_fills()
+{
+    for (LayerRegion *layerm : m_regions)
+        layerm->m_fills.clear();
+    for (LayerSlice &lslice : lslices_ex)
+		for (LayerIsland &island : lslice.islands)
+			island.fills.clear();
+}
+
 void Layer::make_fills(FillAdaptive::Octree* adaptive_fill_octree, FillAdaptive::Octree* support_fill_octree, FillLightning::Generator* lightning_generator)
 {
-	for (LayerRegion *layerm : m_regions)
-		layerm->m_fills.clear();
-
+	this->clear_fills();
 
 #ifdef SLIC3R_DEBUG_SLICE_PROCESSING
 //	this->export_region_fill_surfaces_to_svg_debug("10_fill-initial");

src/libslic3r/Layer.cpp

@@ -443,6 +443,7 @@ void Layer::make_perimeters()
         layerm.m_fill_expolygons_composite_bboxes.clear();
     };
 
+    // Remove layer islands, remove references to perimeters and fills from these layer islands to LayerRegion ExtrusionEntities.
     for (LayerSlice &lslice : this->lslices_ex)
         lslice.islands.clear();
 

src/libslic3r/Layer.hpp

@@ -390,6 +390,8 @@ protected:
         slice_z(slice_z), print_z(print_z), height(height),
         m_id(id), m_object(object) {}
     virtual ~Layer();
+    // Clear fill extrusions, remove them from layer islands.
+    void clear_fills();
 
 private:
     void sort_perimeters_into_islands(

src/libslic3r/PrintObject.cpp

@@ -131,6 +131,7 @@ void PrintObject::make_perimeters()
     // Revert the typed slices into untyped slices.
     if (m_typed_slices) {
         for (Layer *layer : m_layers) {
+            layer->clear_fills();
             layer->restore_untyped_slices();
             m_print->throw_if_canceled();
         }