Seems to be that as part of the layout work the timing sequence for when `.getRoom().widgets` will work changed. We can get around this with `initIfNeeded` which will no-op in the worst case.
This also includes a copy change to make ended conferences stop lying about where to find the widget. This is work towards https://github.com/vector-im/element-web/issues/15739
This should alleviate https://github.com/vector-im/element-web/issues/15705 from happening, though the cause is still unknown.
Requiring a room ID is safe for this because only room widgets can be pinned, and widget IDs are not globally unique which means from a logical standpoint the contract still makes sense here.
