Strip ghost flag from elements on loading

Ghost elements are notoriously a reason of network desyncs, because they
don't get transferred over network. They are meant to be local only and
disregarded by any logic, but it is not yet the case in many places.

Upon saving, we *remove* all the ghost elements (by calling
`scenario_fix_ghosts`), based on assumption they can only be caused by
local interaction. Testing has shown there are `sv6`s in the wild that
have elements marked as ghosts and this could lead to a situation where
we strip away parts of the park. This also causes network desyncs for
reason stated above.

As we strip elements with ghost flag from saves anyway, it should be
safe to assume none of our saves introduce ghosts and this issue is
limited to hacked parks only. One example of such park is [Cocopa
Bay](http://www.nedesigns.com/park/3473/cocopa-bay/).

This change removes the flag on all map elements while importing. This
is much less invasive than removing all ghost elements on importing, as
they may contain some actual data. This ~~fixes~~ hides the desync that
could be seen in the Cocopa Bay park.

As this doesn't change any in-game logic, no network version update is
necessary.

#5094

src/openrct2/rct2/S6Importer.cpp

@@ -364,6 +364,7 @@ void S6Importer::Import()
     {
         throw ObjectLoadException();
     }
+    map_strip_ghost_flag_from_elements();
     map_update_tile_pointers();
     game_convert_strings_to_utf8();
     map_count_remaining_land_rights();

src/openrct2/world/map.c

@@ -429,6 +429,23 @@ void map_count_remaining_land_rights()
 	}
 }
 
+/**
+ * This is meant to strip MAP_ELEMENT_FLAG_GHOST flag from all elements when
+ * importing a park.
+ *
+ * This can only exist in hacked parks, as we remove ghost elements while saving.
+ *
+ * This is less invasive than removing ghost elements themselves, as they can
+ * contain valid data.
+ */
+void map_strip_ghost_flag_from_elements()
+{
+	rct_map_element *mapElement = gMapElements;
+	do {
+		mapElement->flags &= ~MAP_ELEMENT_FLAG_GHOST;
+	} while (++mapElement < gMapElements + 0x30000);
+}
+
 /**
  *
  *  rct2: 0x0068AFFD

src/openrct2/world/map.h

@@ -394,6 +394,7 @@ extern uint8 gUnk9E2E28;
 
 void map_init(sint32 size);
 void map_count_remaining_land_rights();
+void map_strip_ghost_flag_from_elements();
 void map_update_tile_pointers();
 rct_map_element *map_get_first_element_at(sint32 x, sint32 y);
 void map_set_tile_elements(sint32 x, sint32 y, rct_map_element *elements);