Related: fdo#82259 not all STIX are symbol fonts

The new "STIX" and "STIX Math" are regular fonts, as well as the old
"STIXGeneral", so narrow the match a bit.

Change-Id: I82341c3e9e5dd4e0323bf76096cba8890a82f0c7
(cherry picked from commit 56dc7aecc3194dac8012ebc252fb893125f64ebc)
Reviewed-on: https://gerrit.libreoffice.org/10896
Reviewed-by: David Tardon <dtardon@redhat.com>
Tested-by: David Tardon <dtardon@redhat.com>