tdf#75297 sw uno: override default num char style when NONE

The problem was during ODT import. When no text:style-name
is provided, or if it is an empty string, then the default
"Numbering symbols" character style remained active,
preventing the ability to round-trip a NONE char style.

Since this depends on the built-in name
(and that name can easily enough change)
there is not much point in creating a unit test.

Change-Id: Id942060abd3e024758f93f3d279ef8b561cfc5a9
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/134888
Reviewed-by: Justin Luth <jluth@mail.com>
Tested-by: Jenkins
diff --git a/sw/source/core/unocore/unosett.cxx b/sw/source/core/unocore/unosett.cxx
index 5a94663..c68a4fa 100644
--- a/sw/source/core/unocore/unosett.cxx
+++ b/sw/source/core/unocore/unosett.cxx
@@ -1574,10 +1574,11 @@ void SwXNumberingRules::SetPropertiesToNumFormat(
            OUString sCharFormatName;
            SwStyleNameMapper::FillUIName( uTmp, sCharFormatName, SwGetPoolIdFromName::ChrFmt );
            SwDoc *const pLocalDoc = pDocShell ? pDocShell->GetDoc() : pDoc;
            if (sCharFormatName == UNO_NAME_CHARACTER_FORMAT_NONE)
            if (sCharFormatName.isEmpty() || sCharFormatName == UNO_NAME_CHARACTER_FORMAT_NONE)
            {
                rCharStyleName = aInvalidStyle;
                aFormat.SetCharFormat(nullptr);
                aFormat.SetCharFormatName("");
            }
            else if (pLocalDoc)
            {