HPCC-12480 SSL_connect: incorrect use of return value in securesocket

CSecureSocket::secure_connect() is incorrectly checking the return code from
SSL_connect() by ignoring that fact that a return of 0 is also an error. This
fix changes the check from 'if(err < 0)' to 'if(err <= 0)'

Signed-off-by: William Whitehead <william.whitehead@lexisnexis.com>
Merge pull request #6662 from RussWhitehead/secureSock

HPCC-12480 SSL_connect: incorrect use of return value in securesocket

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>