Websocket panic when closing a workspace

[ricklamers]

Log snippet:

2020/04/24 00:20:10 http: panic serving 172.17.0.1:50568: runtime error: invalid memory address or nil pointer dereference
goroutine 66 [running]:
net/http.(*conn).serve.func1(0xc000308000)
	/usr/local/go/src/net/http/server.go:1772 +0x139
panic(0x89e680, 0xe34fb0)
	/usr/local/go/src/runtime/panic.go:975 +0x3e3
main.destructSession(0xc0000f208e, 0x24, 0xc00009ae40, 0xc00009ae70)
	/home/source/proxy/manager.go:217 +0x128
main.main.func16(0x9a3c40, 0xc0001120e0, 0xc000317000)
	/home/source/proxy/manager.go:778 +0xfa
net/http.HandlerFunc.ServeHTTP(0xc0000a63c0, 0x9a3c40, 0xc0001120e0, 0xc000317000)
	/usr/local/go/src/net/http/server.go:2012 +0x44
net/http.(*ServeMux).ServeHTTP(0xe7d6c0, 0x9a3c40, 0xc0001120e0, 0xc000317000)
	/usr/local/go/src/net/http/server.go:2387 +0x1a5
net/http.serverHandler.ServeHTTP(0xc000112000, 0x9a3c40, 0xc0001120e0, 0xc000317000)
	/usr/local/go/src/net/http/server.go:2807 +0xa3
net/http.(*conn).serve(0xc000308000, 0x9a4800, 0xc00030e000)
	/usr/local/go/src/net/http/server.go:1895 +0x86c
created by net/http.(*Server).Serve
	/usr/local/go/src/net/http/server.go:2933 +0x35c
Tried destroying session 3613dcd0-573b-46c0-87b6-2617c1dde6b7, but sessions not in active usersessions.
0 user sessions active.