PR: 1949

Submitted by: David.Smith@cern.ch
Approved by: steve@openssl.org

When checking whether to flush the output BIO use BIO_CTRL_WPENDING instead
of BIO_CTRL_INFO. In most cases this will have no effect since the following
BIOs wont buffer. In the case of a following buffering BIO this will check
for any pending data in the whole chain and not just the single BIO.

See:
https://issues.apache.org/bugzilla/show_bug.cgi?id=46952
for a detailed analysis of this issue.