Simplify some operation involving OUString and OUStringBuffer

Change-Id: I147386464662eb9cad7bcf10cd0d7e6df07cfcf8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/101577
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>
diff --git a/oox/source/dump/dumperbase.cxx b/oox/source/dump/dumperbase.cxx
index 8fcb727..aac2af5 100644
--- a/oox/source/dump/dumperbase.cxx
+++ b/oox/source/dump/dumperbase.cxx
@@ -1595,7 +1595,7 @@ void Output::endItem()
{
    if( mnItemLevel > 0 )
    {
        maLastItem = OUString( maLine.getStr() + mnLastItem );
        maLastItem = maLine.copy( mnLastItem ).makeStringAndClear();
        if( maLastItem.isEmpty() && mnLastItem > 0 && maLine[ mnLastItem - 1 ] == OOX_DUMP_ITEMSEP )
            maLine.setLength( mnLastItem - 1 );
        --mnItemLevel;