Merge branch 'master' into jgrpp

# Conflicts:
#	.gitignore
#	CMakeLists.txt
#	src/3rdparty/optional/optional.hpp
#	src/group_cmd.cpp
#	src/industry_cmd.cpp
#	src/misc_gui.cpp
#	src/video/sdl2_v.cpp

src/saveload/engine_sl.cpp

@@ -191,8 +191,7 @@ static void Load_EIDS()
 	_engine_mngr.clear();
 
 	while (SlIterateArray() != -1) {
-		/*C++17: EngineIDMapping *eid = &*/ _engine_mngr.emplace_back();
-		EngineIDMapping *eid = &_engine_mngr.back();
+		EngineIDMapping *eid = &_engine_mngr.emplace_back();
 		SlObject(eid, _engine_id_mapping_desc);
 	}
 }