Fix failure to remove expired walls

std::remove_if can be called on an iterator that returns a proxy object,
but the results of that call are not generally useful.  When remove_if
attempts to move-assign over removed elements, it instead assigns over
the temporary proxy object.  If the proxy object has typical move
semantics, move-assigning over it has no effect on the underlying
container.

Revert to using partial_range on the underlying container.

Reported-by: Mako88 <#283>
Fixes: 1f434f9 ("Use valptridx for ActiveDoors")

similar/main/wall.cpp

@@ -1240,14 +1240,14 @@ namespace dsx {
 void wall_frame_process()
 {
 	{
-		const auto &&r = make_range(vactdoorptr);
+		const auto &&r = partial_range(ActiveDoors, ActiveDoors.get_count());
 		auto &&i = std::remove_if(r.begin(), r.end(), ad_removal_predicate());
 		ActiveDoors.set_count(std::distance(r.begin(), i));
 	}
 #if defined(DXX_BUILD_DESCENT_II)
 	if (Newdemo_state != ND_STATE_PLAYBACK)
 	{
-		const auto &&r = make_range(vclwallptr);
+		const auto &&r = partial_range(CloakingWalls, CloakingWalls.get_count());
 		cw_removal_predicate rp;
 		std::remove_if(r.begin(), r.end(), std::ref(rp));
 		CloakingWalls.set_count(rp.num_cloaking_walls);