DisconnectClient cause panic

[selimanac]

When 3th connection disconnects:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x10 pc=0x1285132]

goroutine 35 [running]:
github.com/selimanac/goreal.(*RoomManager).DisconnectClient(0x0, 0xc00018e0a0)
        /Users/selimanac/go/src/github.com/selimanac/goreal/room_manager.go:95 +0x22
github.com/selimanac/goreal.(*GameServer).DisconnectClient(0xc00000e360, 0xc00018e0a0)
        /Users/selimanac/go/src/github.com/selimanac/goreal/server.go:140 +0xf4
github.com/selimanac/goreal.(*Hub).run(0xc000090020, 0xc00000e360)
        /Users/selimanac/go/src/github.com/selimanac/goreal/hub.go:43 +0x332
created by github.com/selimanac/goreal.(*GameServer).Start
        /Users/selimanac/go/src/github.com/selimanac/goreal/server.go:38 +0x15b
exit status 2
The terminal process terminated with exit code: 1