Never ending progress when forgetting to register custom editor provider

[alexdima]

Testing #96315

• Have an extension with the following package.json:

    ...
    "activationEvents": [
        "onCustomEditor:my.custom.editor"
    ],
    ...
    "contributes": {
        "customEditors": [
            {
                "viewType": "my.custom.editor",
                "displayName": "My Custom Editor",
                "selector": [
                    {
                        "filenamePattern": "*.bin"
                    }
                ]
            }
        ]
    }

• Have the extension have a main file with an activate method that doesn't do anything
• Open a file with the extension .bin:
• Observe, there is a spinner that never stops and no message is presented to informat that an editor is missing or cannot be loaded:

[mjbvz]

Closing this since we have not seen reports of it causing problems for users. This is also the behavior of normal webviews