websocket: fix nil pointer in tlsClientConf

[MarcoPolo]

It's possible (and common) to have a WebSocket transport without a tls client config. This leads to a nil pointer deref error when we set the ServerName.

This sets a default empty tlsClientConf and adds a test case.

Fixes https://github.com/libp2p/go-libp2p/issues/1769

[github-actions[bot]]

Suggested version: v0.23.1 Comparing to: v0.23.0 (diff)

Changes in go.mod file(s):

(empty)

gorelease says:

# diagnostics
go.mod: the following requirements are needed
	github.com/libp2p/go-yamux/[email protected]
Run go mod tidy to add missing requirements.
required module github.com/microcosm-cc/[email protected] retracted by module author: Retract older versions as only latest is to be depended upon

# summary
Suggested version: v0.23.1

gocompat says:

(empty)

[marten-seemann]

I removed the release commit. Let's first make sure we can build kubo before cutting a patch release.