UB when editor is launched

[matthiaskrgr]

wesnoth @ d9d67f0

 UBSAN_OPTIONS=print_stacktrace=1 ./build/wesnoth -e
Battle for Wesnoth v1.13.11 (d9d67f0b95-Clean)
Started on Mon Feb  5 14:58:04 2018

Automatically found a possible data directory at /home/matthias/vcs/github/wesnoth/build/..

Data directory:               /home/matthias/vcs/github/wesnoth/build/..
User configuration directory: /home/matthias/.config/wesnoth
User data directory:          /home/matthias/.local/share/wesnoth/1.13
Cache directory:              /home/matthias/.cache/wesnoth

Setting mode to 800x860
Checking lua scripts... ok
../src/game_display.hpp:47:10: runtime error: downcast of address 0x61e0000e7080 which does not point to an object of type 'game_display'
0x61e0000e7080: note: object is of type 'editor::editor_display'
 55 00 80 01  d0 b2 bc 00 00 00 00 00  01 00 be be 00 00 00 00  80 f4 1a 00 d0 61 00 00  10 5c 3c 00
              ^~~~~~~~~~~~~~~~~~~~~~~
              vptr for 'editor::editor_display'
    #0 0x521e7bc in game_display::get_singleton() /home/matthias/vcs/github/wesnoth/build/../src/game_display.hpp:47:10
    #1 0x96a0e2c in image::getMinimap(int, int, gamemap const&, team const*, std::map<map_location, unsigned int, std::less<map_location>, std::allocator<std::pair<map_location const, unsigned int> > > const*, bool) /home/matthias/vcs/github/wesnoth/build/../src/minimap.cpp:87:27
    #2 0x923a63c in display::draw_minimap() /home/matthias/vcs/github/wesnoth/build/../src/display.cpp:1803:14
    #3 0x923837a in display::draw_wrap(bool, bool) /home/matthias/vcs/github/wesnoth/build/../src/display.cpp:1700:3
    #4 0x9217cfe in display::draw(bool, bool) /home/matthias/vcs/github/wesnoth/build/../src/display.cpp:2520:2
    #5 0x921963a in display::redraw_everything() /home/matthias/vcs/github/wesnoth/build/../src/display.cpp:2449:2
    #6 0x5aa88e0 in editor::editor_controller::editor_controller(config const&) /home/matthias/vcs/github/wesnoth/build/../src/editor/controller/editor_controller.cpp:89:8
    #7 0x5968a32 in editor::start(config const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) /home/matthias/vcs/github/wesnoth/build/../src/editor/editor_main.cpp:36:21
    #8 0x51bc97d in game_launcher::start_editor(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) /home/matthias/vcs/github/wesnoth/build/../src/game_launcher.cpp:1004:29
    #9 0x51bc32f in game_launcher::goto_editor() /home/matthias/vcs/github/wesnoth/build/../src/game_launcher.cpp:757:7
    #10 0x4ec2323 in do_gameloop(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&) /home/matthias/vcs/github/wesnoth/build/../src/wesnoth.cpp:827:12
    #11 0x4ebc9eb in main /home/matthias/vcs/github/wesnoth/build/../src/wesnoth.cpp:1150:19
    #12 0x7fe33a0a6889 in __libc_start_main (/lib64/libc.so.6+0x20889)
    #13 0x4de6029 in _start (/home/matthias/vcs/github/wesnoth/build/wesnoth+0x4de6029)

SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../src/game_display.hpp:47:10 in