Resolves: tdf#93317 Modified Document Dialog misses focus on Gtk3

Change-Id: I16ddac82a76a1e665797e4be192d3642f2660d9f
(cherry picked from commit 82abd23f)
Reviewed-on: https://gerrit.libreoffice.org/19933Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Adolfo Jayme Barrientos <fitojb@ubuntu.com>

vcl/source/window/dialog.cxx

@@ -816,6 +816,7 @@ bool Dialog::ImplStartExecuteModal()
     ImplAdjustNWFSizes();
 
     Show();
+    ToTop();
 
     pSVData->maAppData.mnModalMode++;
     return true;