Fof flag change hotfix

This fixes rendering issues caused by changing FOF flags mid-level via Lua or linedef type 445. Everything else that toggles FF_EXISTS already had this fix it turns out.

Not sure if this is safe for master too, could someone check that for me?

src/lua_maplib.c

@@ -1111,9 +1111,13 @@ static int ffloor_set(lua_State *L)
case ffloor_bottompic:
*ffloor->bottompic = P_AddLevelFlatRuntime(luaL_checkstring(L, 3));
break;
-	case ffloor_flags:
+	case ffloor_flags: {
+		ffloortype_e oldflags = ffloor->flags; // store FOF's old flags
ffloor->flags = luaL_checkinteger(L, 3);
+		if (ffloor->flags != oldflags)
+			ffloor->target->moved = true; // reset target sector's lightlist
break;
+	}
case ffloor_alpha:
ffloor->alpha = (INT32)luaL_checkinteger(L, 3);
break;