Fix WebSocketServer sometimes missing GET request

On Ubuntu 22.04 with Linux 6.5, it was observed that when the server
gets the SSL records containing the client handshake finished message
and the first HTTP GET request in ONE read operation, the latter SSL
record is never processed.

Commit 89eaf410dd8fe3845fa6fb0de3469b55da0205cb should have fixed this,
but it turned out that when SSLSocketChannel2#processHandshake() is
called from SSLSocketChannel2#write(), the second SSL record containing
the HTTP GET request is stashed away, but never retrieved, since the
calling code in WebSocketServer#doWrite() has no provisions for this,
only WebSocketServer#doRead() does.

Change SSLSocketChannel2#processHandshake() to only read from the socket
when called from SSLSocketChannel#read(), to ensure that when two SSL
records are read, the second one is processed as well.

This fixes issue #1418.