Problem description:

**Imagine that You have 2 graph, or graph prototype widgets on the dashboard, each of them displaying a graph that the other cannot display for a certain host (the host doesn't have such graph). Then the user performs the following actions:

1 - user selects a host that doesn't have the graph that one of the widgets is supposed to display
2 - then he open the dashboard in edit mode and updates the widget (for example hides widget header)
3 - then he edits the dashboard again and once again updates the widget (for example returns widget header setting to its initial state)

In this case, while the dashboard is in edit mode for the 1st time, the widget will display the graph that was set in widget configuration form (ignores the dynamic widget field), but on 2nd edit (after the page was refreshed by applying previous changes) the widget displays a message, informing the user that the object doesn't exist (it takes into account the dynamic widget field value).

Steps to reproduce:

1. Create 3 hosts
2. Host #1 and Host #2 should have a common graph (or graph prototype)
3. Host #2 and Host #3 should have a common graph (or graph prototype)
4. Create a new dashboard and add 2 dynamic graph (or graph prototype) widgets
5. 1st widget should display the graph that is common for Host #1 and Host #2
6. 2nd widget should display the graph that is common for host #2 and Host #3
7. In the dynamic widget field select Host #2 - both graphs are displaying data.
8. Select Host #1 in the dynamic widget field - only 1st widget displays data.
9. Edit dashboard by clicking on the cogwheel icon on the 2nd widget
10. Remove (or set) the "Show header" checkboxin widget config form and press "Apply" button.
    Result 1: Until the user exits dashboard edit mode, the widget displays the graph that was set in widget configuration form, ignoring the value set in dynamic widget field.
11. Save the dashboard - notice that in widget #2 a message is shown stating that the corresponding object doesn't exist.
12. Edit dashboard by clicking on the cogwheel icon on the 2nd widget
13. Remove (or set) the "Show header" checkbox in widget config form and press "Apply" button.
    Result 2: Now also in dashboard edit mode the widget displays a message that the object doesn't exist (as per the value set in dynamic widget field).

Expected: The widget should work consistently - either it should display the message or it should display the graph that is set in widget config.

 
Example: