Resolves: tdf#85979 TextToColumns is overwriting, so set at ScImportExport

Change-Id: Id0fec512b53aab47f9951056e8726af0cce45708
(cherry picked from commit 624ab2e5)
Reviewed-on: https://gerrit.libreoffice.org/18664Reviewed-by: Markus Mohrhard <markus.mohrhard@googlemail.com>
Tested-by: Markus Mohrhard <markus.mohrhard@googlemail.com>

sc/source/ui/view/cellsh2.cxx

@@ -979,6 +979,7 @@ void ScCellShell::ExecuteDB( SfxRequest& rReq )
                         aImport.SetExtOptions( aOptions );
                         aImport.SetApi( false );
                         aImport.SetImportBroadcast( true );
+                        aImport.SetOverwriting( true );
                         aStream.Seek( 0 );
                         aImport.ImportStream( aStream, OUString(), SotClipboardFormatId::STRING );