Fix crash when switching from a level with lightmaps to one without

src/rendering/hwrenderer/doom_levelmesh.cpp

@@ -238,6 +238,10 @@ DoomLevelMesh::DoomLevelMesh(FLevelLocals& doomMap)
 	r_viewpoint.camera = oldcamera;
 }
 
+DoomLevelMesh::~DoomLevelMesh()
+{
+}
+
 void DoomLevelMesh::SetLimits(FLevelLocals& doomMap)
 {
 	// Try to estimate what the worst case memory needs are for the level

src/rendering/hwrenderer/doom_levelmesh.h

@@ -90,6 +90,7 @@ class DoomLevelMesh : public LevelMesh, public UpdateLevelMesh
 {
 public:
 	DoomLevelMesh(FLevelLocals &doomMap);
+	~DoomLevelMesh();
 
 	void PrintSurfaceInfo(const LevelMeshSurface* surface);