Check form is valid in update path callback

https://app.getsentry.com/gostellarorg/stellar-client/group/35926009/
https://app.getsentry.com/gostellarorg/stellar-client/group/35927479/

This is not the correct fix.

The core issue is that the live form variables are being used for validation instead of the cloned copy. Also, when the input changes, this update listener should have been canceled.

Instead of adding more hacks we should prioritize refactoring this controller.