Problem description: As per design, it should not be possible to submit widget configuration form, if it is listening for a Host group, Host or an Item from an unavailable widget. This works fine for all existing widget types except for SVG graph and Pie chart widgets - for those widgets the form is successfully submitted:

Steps to reproduce:

1. Create a dashboard with the following widgets:
   1. A honeycomb widget that displays some item
   2. An SVG graph widget that listens to the item selected in the honeycomb widget
   3. A Pie chart widget that listens to the item selected in the honeycomb widget
2. Save dashboard configuration
3. Edit dashboard and delete the honeycomb widget
4. Make sure that both SVG graph and Pie chart widgets state that the referred widget is not available.
5. Open configuration of the SVG graph and Pie chart widgets one by one and attempt to submit the opened form it without any changes

Result: form is successfully submitted. No errors are displayed
Expected: form should not be submitted. An error, stating that field contains an invalid parameter and that refered widget is not available, should be displayed.