Joining 127.0.0.1 while no server is running crashes the game

[ITR13]

Stacktrace:

[info]: Blue noise took 52 ms to load
[info]: Framebuffer: 1280, 720
[info]: [censored]
[info]: User #00ffffITR joined using version Cubyz ╬▒ 0.12.0.
thread 15296 panic: attempt to use null value
D:\source\Cubyz\src\network.zig:682:111: 0xca6909 in receive (Cubyzig.exe.obj)
       const path = std.fmt.allocPrint(main.stackAllocator.allocator, "saves/{s}/assets/", .{main.server.world.?.name}) catch unreachable;
                                                                                                              ^
D:\source\Cubyz\src\network.zig:1732:14: 0xf87d60 in collectPackets (Cubyzig.exe.obj)
     try prot(self, data);
             ^
D:\source\Cubyz\src\network.zig:1781:27: 0xf88941 in flawedReceive (Cubyzig.exe.obj)
   try self.collectPackets();
                          ^
D:\source\Cubyz\src\network.zig:1741:21: 0xf3b5b2 in receive (Cubyzig.exe.obj)
  self.flawedReceive(data) catch |err| {
                    ^
D:\source\Cubyz\src\network.zig:561:18: 0xed66be in onReceive (Cubyzig.exe.obj)
     conn.receive(data);
                 ^
D:\source\Cubyz\src\network.zig:592:19: 0xe620c5 in run (Cubyzig.exe.obj)
    self.onReceive(data, source);
                  ^
D:\source\Cubyz\compiler\zig\lib\std\Thread.zig:408:13: 0xdd780c in callFn__anon_56139 (Cubyzig.exe.obj)
            @call(.auto, f, args);
            ^
D:\source\Cubyz\compiler\zig\lib\std\Thread.zig:518:30: 0xd4323f in entryFn (Cubyzig.exe.obj)
                return callFn(f, self.fn_args);
                             ^
???:?:?: 0x7ffe4a697373 in ??? (KERNEL32.DLL)
???:?:?: 0x7ffe4b05cc90 in ??? (ntdll.dll)

[censored] was my public IP, the one shown above the 127.0.0.1 box.

[IntegratedQuantum]

related: #264