WebTable: Fix a javascript error when using single mode and radio buttons.

[GB.WEB.GUI]
* BUG: WebTable: Fix a javascript error when using single mode and radio buttons.

comp/src/gb.web.gui/lib.js

@@ -1306,7 +1306,7 @@ gw = {
       else
         gw.table.checkRange(id, row, row, checked);
       
-      if (event.target == elt)
+      if (event && event.target == elt)
         elt.checked = !checked;
 
       $_(id).gw_current = row;