Viewer.destroy not checking if ScreenSpaceEventHandler is defined

[TJPovey]

Sandcastle example:
https://sandcastle.cesium.com/#c=hVA9a8MwEP0rhztYhiDTuY4ppIUOgQ6BTl4U6ZqKyJIrnRzc0v9eOUogoYFqu/dx7+mks4Fg1HhAD0uweIAVBh17/nbEWFfI47xyloS26LuieuhsZ7OHB+kR7WYQEp9HtPQirDIJVxjIu4llsXIy9onlnxH9tEGDkpxn5d1JlsPKiguljmvWOhCmNFZKo+W+XACrYNnCd2cBZCrtDHLjduyfGjo85QRUrJq7wOmzVwV/cstiUTSBJoPtrJvfo+4H5wmiN4zzmrAfjCAM9TbKPRKXIeSlAE19aW2UHkGr5Y3zgTQihMS8R2M2+gu7om3qpP9jNU4obXevI3ojpln2cd+uM8g5b+o03naSc2YrUtiZ2UYiZzN5dfMkOV0IMtDUWXt2Xuz/BQ

If the viewers ScreenSpaceEventHandler has been destroyed prior to the viewer being destroyed, unminifed cesiumjs is throwing a developer error:
The object is destroyed...
The viewers destroy method is not checking if the handler has been destroyed prior to using it, like it is for other fields:

cesium/Source/Widgets/Viewer/Viewer.js

Line 1681 in 51f3c65

this.screenSpaceEventHandler.removeInputAction(

Happy to create a PR or remove the issue if it is desired behaviour. Although it does look like the viewer is only removing two input actions and not actually destroying the handler:

  this.screenSpaceEventHandler.removeInputAction(
    ScreenSpaceEventType.LEFT_CLICK
  );
  this.screenSpaceEventHandler.removeInputAction(
    ScreenSpaceEventType.LEFT_DOUBLE_CLICK
  );

[ggetz]

@TJPovey Thanks for the report! Though I think there was an underlying assumption that the screenSpaceEventHandler wouldn't be destroyed separately, I don't see why a simple verification in the destroy method would hurt.

[nayangoyal]

Hi, @ggetz can you assign this issue to me? I want to work on this issue.

[ggetz]

Hi @nayangoyal, great! Please go ahead and get started by taking a look at CONTRIBUTING.md.