schannel SSL: changes in schannel_connect_step2

Process extra data buffer before returning from schannel_connect_step2.
Without this change I've seen WinCE hang when schannel_connect_step2
returns and calls Curl_socket_ready.

If the encrypted handshake does not fit in the intial buffer (seen with
large certificate chain), increasing the encrypted data buffer is necessary.

Fixed warning in curl_schannel.c line 1215.