filter: PDF Export UI "page range" autofocus

When the user selects "Pages" radio button in the Range section, it is very
reasonable to expect that she would now want to specify the range. Thus moving
the focus automatically to the page range edit box would save the user a mouse
click.a

Code is contributed under the LGPLv3+ / MPL.

filter/source/pdf/impdialog.cxx

@@ -651,6 +651,8 @@ IMPL_LINK( ImpPDFTabGeneralPage, TogglePagesHdl, void*, EMPTYARG )
     maEdPages.Enable( maRbRange.IsChecked() );
     //Sym2_5805, When the control is disabled, it is also readonly. So here, it is not necessary to set it as readonly.
     //maEdPages.SetReadOnly( !maRbRange.IsChecked() );
+    if ( maRbRange.IsChecked() )
+        maEdPages.GrabFocus();
     return 0;
 }