wings: fix runtime failure. (#48681)

Erlang/OTP 18 [erts-7.3.1.4] [source] [64-bit] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V7.3.1.4  (abort with ^G)
1>
=ERROR REPORT==== 18-Oct-2018::21:29:53 ===
beam/beam_load.c(1189): Error loading module sdl:
  mandatory chunk of type 'Atom' not found

=ERROR REPORT==== 18-Oct-2018::21:29:53 ===
Loading of /nix/store/qalvdrzjqqm3a8nsavjbhfiv1pzhw82k-esdl-1.3.1/lib/erlang/lib/esdl-1.3.1/ebin/sdl.beam failed: badfile

=ERROR REPORT==== 18-Oct-2018::21:29:53 ===
Error in process <0.35.0> with exit value:
{undef,[{sdl,init,[1048608],[]},
        {wings_init,init,0,[{file,"wings_init.erl"},{line,28}]},
        {wings,init,1,[{file,"wings.erl"},{line,105}]}]}

Fatal internal error - log written to /home/milan/wings_crash.dump