Use SSL_get_error, not SSL_write rc for SSL_ERROR_WANT_* check

[na-gupta]

Description

Based on OpenSSL documentation, when SSL_write and SSL_read return a negative return code, we should use SSL_get_error to get the error code to compare with SSL_ERROR_WANT_READ and SSL_ERROR_WANT_READ.

Testing SSL_ERROR_WANT_READ and SSL_ERROR_WANT_READ (which are both positive values) against a negative return value of SSL_write and SSL_read will never return true.

This same change also needs to be done in SSLService.recv() after SSL_read. But when I tried that, Socket.isReadableOrWritable() kept returning false and so wait(forRead:) looped forever and caused the request to hang. It probably needs some additional fixes there before the SSLService.recv() fix can be done.

Motivation and Context

Kitura/Kitura#1036

How Has This Been Tested?

Checklist:

• I have submitted a CLA form
• If applicable, I have updated the documentation accordingly.
• If applicable, I have added tests to cover my changes.

[billabt]

Rejecting this PR in favor of a more comprehensive fix.