Set initial focus to the 'Open XML source' button.

This helps with keyboard-only navigation in this dialog.

Change-Id: Ie3d580ba921c93ae256ad0a503615de7a037323a

sc/source/ui/xmlsource/xmlsourcedlg.cxx

@@ -105,6 +105,7 @@ ScXMLSourceDlg::ScXMLSourceDlg(
     maRefEdit.SetModifyHdl(aLink);
 
     SetNonLinkable();
+    maBtnSelectSource.GrabFocus();
 }
 
 ScXMLSourceDlg::~ScXMLSourceDlg()