Qt: Workaround the bug of preference height on small screens

Close #3884

modules/gui/qt4/dialogs/preferences.cpp

@@ -111,7 +111,7 @@ PrefsDialog::PrefsDialog( QWidget *parent, intf_thread_t *_p_intf )
     tree_panel_l->setMargin( 1 );
     main_panel_l->setContentsMargins( 6, 0, 0, 3 );
 
-    b_small = (p_intf->p_sys->i_screenHeight < 750);
+    b_small = (p_intf->p_sys->i_screenHeight < 850);
     if( b_small ) msg_Dbg( p_intf, "Small");
     setMaximumHeight( p_intf->p_sys->i_screenHeight );
     for( int i = 0; i < SPrefsMax ; i++ ) simple_panels[i] = NULL;