io.sockets.secure.openssl: fix when SSL_read returns 0.

io.sockets.secure.openssl: fix when SSL_read returns 0.

SSL_read returns 0 which is an error condition, and SSL_get_error
returns 6 which is SSL_ERROR_ZERO_RETURN. In this case, we just need
to do nothing instead of setting ``f >>connected`` which would cause
the socket to attempt a reconnect.

test case:
USE: gemini
"gemini://gemini.circumlunar.space" gemini.

Fixes #2540