Make sure that our normal SAL_WARN() reporting is registered during the
xmlSecCheckVersionExt() invocation, just like it's registered during
other libxmlsec API calls.

(cherry picked from commit 099ab643)

Change-Id: Ia19368b55dbae47974f48954f86b50e36d1462ff
Reviewed-on: https://gerrit.libreoffice.org/64626
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>