Nullpointer access:
```
(gdb) bt
#0 __strlen_sse2 () at ../sysdeps/x86_64/multiarch/../strlen.S:120
#1 0x0000556e5ee1ba5d in str_length (str=str@entry=0x0) at /home/teeworlds/src7/master/src/base/system.c:1833
#2 0x0000556e5edca5c0 in CGameContext::LoadMapSettings (this=this@entry=0x7fd802d31010)
at /home/teeworlds/src7/master/src/game/server/gamecontext.cpp:2355
#3 0x0000556e5edcac8d in CGameContext::OnInit (this=0x7fd802d31010)
at /home/teeworlds/src7/master/src/game/s...