Changing scene to Hubs Room URL instead of Scene URL breaks room

[emclaren]

Description
When you change the scene using the "/scene" command, if you use a URL that links to a Hubs Room instead of a Scene by mistake, the room breaks and will no longer load.

It throws an error that says "SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data"

To Reproduce
Steps to reproduce the behavior:

1. Go to Hubs room
2. type /scene
3. Refresh the page, it will no longer load

Expected behaviour
I expect the scene to not change, and when I refresh the scene it will remain as the last-used scene, or just a big empty room. I do not expect it to make the room URL break.

Additional context
This error happened to Elgin while testing out scenes, but it has also been flagged by the community

[misslivirose]

Given that this fairly catastrophically impacts the room, I think it would be good to handle this in a way that doesn't break the room.

[emclaren]

Just realized as well - there is no way of removing a room that was broken like this from the list of favourites (since you need to open the room to favourite/unfavourite). My list is stuck looking like this

[misslivirose]

@emclaren just opened a new issue for removing favorites (#1912 )

[misslivirose]

When we fix this, we should incorporate the suggestions in #811 as well in terms of general error messaging back to the user when a URL isn't going to work.