Error when loading Reader on hash corresponding to off-screen item

[boonebgorges]

When loading the Reader using a hash corresponding to an item that doesn't appear in the displayed list of items, the JS application can't fully initialize. More specifically:

1. Load /wp-admin/admin.php?page=pf-menu&pc=1#modal-4393b94dda497e63a0b0d62f2b488d24, where 4393b94dda497e63a0b0d62f2b488d24 is the hash of an item that appears on page 2+.
2. You'll see the following stack trace in the browser console: https://gist.github.com/boonebgorges/2b14518de700ad5f48a81c8b605ea4d4

When bisecting back to before the Bootstrap 5 update, the behavior changes somewhat: you don't see an error, but the modal doesn't load. So this is a problem that's likely existed since the introduction of the Reader.

I assume the issue is that the item's markup doesn't appear in the DOM, which means that the modal can't be initialized. A "proper" fix might involve building the modals in such a way that we don't need to have the markup in the DOM on the pageload. But this is not only a big technical change, but we then have to ask how the user will be dropped into pagination/infiniteScroll in that situation. (Should they be dropped onto page 15/100 if that's where the item appears? If infiniteScroll, should they see the first 15*20 items?)

In the short term, I think we could redirect away from the hash when the corresponding element isn't found on the page, which will at least prevent the JS application from seizing up.

[boonebgorges]

Related: #1184