CONC-693 Fix SSL_read/write return value checking in ma_tls_async_check_result

[joshuahunt]

SSL_{read,write}'s return values == 0 signify the operation was unsuccessful, but here it's being treated as success. Other calls of these functions already properly checks the return value.

Please note I found this through code inspection while trying to debug a different issue. I do not have a case where this can be hit, but in principle this should be fixed. Link to openssl man page showing return values <= 0 signify an error https://www.openssl.org/docs/manmaster/man3/SSL_read.html

[joshuahunt]

It looks like this commit fixed the problem for ma_tls_read() but missed it for ma_tls_async_check_result() @9E0R9

commit f1b08b836931daf5b20405b567a6dee2d6a89400
Author: Georg Richter <[email protected]>
Date:   Fri Jul 8 07:46:00 2022 +0200

    Partial fix for MDEV-27405:
    
    The return value of SSL_read indicates an error if it is <= 0, not
    if it is < 0.

[9EOR9]

Thanks for your pull request! Could you please provide the PR against 3.1 branch (still included in Server 10.5), I will then merge it from 3.1 into 3.4 (3.3 will be disontinued).

[joshuahunt]

Thanks for your pull request! Could you please provide the PR against 3.1 branch (still included in Server 10.5), I will then merge it from 3.1 into 3.4 (3.3 will be disontinued).

OK I rebased it on top of 3.1. Please let me know if there's anything else you need me to do.