User API keys: duplicate client_id will lead to internal server error

When calling user-api-key/new with a client_id that is already used by another user the forum will throw a RecordNotUnique error and silently fail on an internal server error.

ActiveRecord::RecordNotUnique (PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_user_api_keys_on_client_id"
DETAIL:  Key (client_id)=(893e0230d52455ea9b729334) already exists.
(eval):105:in `exec_params'
app/controllers/user_api_keys_controller.rb:66:in `create'

This might want to fail with something less silent informing the user that there already exists an API key with that client ID.

Though that brings me on the second question, are User API keys supposed to behave like that? Is the client ID supposed to be unique between all users?