ChangeEmailModal: dismiss alert on new request
ChangeEmailModal: dismiss alert on new request

Removing old errors at the beginning of the next request, rather than at the end of the next successful request, makes it clearer that any new errors are caused by the new inputs.

See https://github.com/flarum/core/pull/2467#issuecomment-749832787

flarum/core,flarum/core,flarum/core