Temporary fix for segfault (#1697)

Sometimes, objects being deleted from a sector (e.g. exploding bombs) remained referenced in CollisionObjects and were accessed despite not existing.

The fix works but is not really nice. It will be improved as part of a larger work on code quality.

Closes #1695

src/collision/collision_object.cpp

@@ -66,6 +66,12 @@ CollisionObject::collision_moving_object_bottom(CollisionObject& other)
   }
 }
 
+void
+CollisionObject::notify_object_removal(CollisionObject* other)
+{
+  m_objects_hit_bottom.erase(other);
+}
+
 void
 CollisionObject::clear_bottom_collision_list()
 {

src/collision/collision_object.hpp

@@ -54,6 +54,8 @@ class CollisionObject
   /** called when this object, if (moving) static, has collided on its top with a moving object */
   void collision_moving_object_bottom(CollisionObject& other);
 
+  void notify_object_removal(CollisionObject* other);
+
   void set_ground_movement_manager(const std::shared_ptr<CollisionGroundMovementManager>& movement_manager)
   {
     m_ground_movement_manager = movement_manager;

src/collision/collision_system.cpp

@@ -56,6 +56,14 @@ CollisionSystem::remove(CollisionObject* object)
   m_objects.erase(
     std::find(m_objects.begin(), m_objects.end(),
               object));
+
+  // FIXME: this is a patch. A better way of fixing this is coming.
+  for (auto* collision_object : m_objects) {
+    collision_object->notify_object_removal(object);
+  }
+  for (auto* tilemap : m_sector.get_solid_tilemaps()) {
+    tilemap->notify_object_removal(object);
+  }
 }
 
 void

src/object/tilemap.cpp

@@ -535,6 +535,12 @@ TileMap::hits_object_bottom(CollisionObject& object)
   m_objects_hit_bottom.insert(&object);
 }
 
+void
+TileMap::notify_object_removal(CollisionObject* other)
+{
+  m_objects_hit_bottom.erase(other);
+}
+
 void
 TileMap::set_solid(bool solid)
 {

src/object/tilemap.hpp

@@ -131,6 +131,7 @@ class TileMap final :
   /** Called by the collision mechanism to indicate that this tilemap has been hit on
       the top, i.e. has hit a moving object on the bottom of its collision rectangle. */
   void hits_object_bottom(CollisionObject& object);
+  void notify_object_removal(CollisionObject* other);
 
   int get_layer() const { return m_z_pos; }
   void set_layer(int layer_) { m_z_pos = layer_; }