Sending to the same LN invoice UX improvement

[catch-21]

Raised off the back of #1488

When attempting to spend the same LN invoice an ugly error is displayed later in the flow than is ideal.

https://github.com/synonymdev/bitkit/assets/74595920/30ea7ba2-13d4-4bf7-8014-249135a1d5c2

It would be an improvement to not allow the user to get this far. Instead, detect the invoice is already spent at the time of scan or input and present a toast to communicate the fact (similar to Pheonix).