Fixed an issue where supplying an emtpy host to the Client TLS handler would result in an SNI error

Motivation:

Testing on Linux seemed to reveal an `NIOSSLExtraError.invalidSNIHostname` error that was thrown when using `https+unix` URLs, which don't have their hostname filled in. The same NIO failure does not occur on macOS.

Modifications:

Added an extra check to determine if the host is empty before passing it to a `NIOSSLClientHandler`.

Result:

Hopefully one fewer test failures on Linux

Author: dimitribouniol

Sources/AsyncHTTPClient/HTTPClient.swift

@@ -665,7 +665,7 @@ extension ChannelPipeline {
                 let tlsConfiguration = tlsConfiguration ?? TLSConfiguration.forClient()
                 let context = try NIOSSLContext(configuration: tlsConfiguration)
                 handlers = [
-                    try NIOSSLClientHandler(context: context, serverHostname: key.host.isIPAddress ? nil : key.host),
+                    try NIOSSLClientHandler(context: context, serverHostname: key.host.isIPAddress || key.host.isEmpty ? nil : key.host),
                     TLSEventsHandler(completionPromise: handshakePromise),
                 ]
             } else {