"LC_ALL=C make CppunitTest_sw_rtfexport" was still failing after
e47a02b1 "fdo#77979: sw: RTF export: write non-
ASCII font names encoded," so for each given eTextEncoding determine a Windows
charset that can at least encode the font's name, and not only for Unicode-
related eTextEncodings.

Change-Id: If547566bb0cffc60411d8f667d76749a904f7a3f
(cherry picked from commit 0dc7d636)
Reviewed-on: https://gerrit.libreoffice.org/9762Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>