Chat: Allow both the submitting and "next" input to cancel the submission.

[RXminuS]

Right now after submitting a message you have to chase the "stop" button around as text is generated. This change ensures that both the submitting and follow up field give a way to cancel the message.

Not the most elegant fix, but patches a frustration @dominiccooney and @abeatrix shared until we can maybe think of something more slick.

Test plan

CI