Adding an empty state mapping and then editing it causes state mapping duplicity

Issue Summary

If the user clicks on the 'Add' button from the State Mapping page without selecting any state, it will create a temporary state that could allow users to bulk editing/adding states.
The problem is that the user will be able to enter a value that already exists or will be imported from Jira.

As the state is duplicated, it will appear twice in the State Mapping, and in the Manage Custom Fields, where it won't save for the duplicated items.

Steps to Reproduce

1. In Jira Settings -> State Mapping, choose a type (e.g. Feature) click on the 'Add' button;
2. Choose the newly created item: *Configure New Jira State* and then give it an existing ID (ID that is not currently selected/listed for mapping), name and choose any Jira Align State;
3. Save
4. Now if you click on the selection field, the status will be displayed twice.

Expected Results

To not be able to have duplicated Jira State IDs (as the normal save prevents it).

Actual Results

It's possible to create a duplicated Jira State ID. It's possible to create with an existing ID or even creating an ID that will be synced from Jira in the future, causing duplicities and making it impossible to save the changes in the Manage Custom Fields page.

Workaround

There is no workaround once the Jira state is mapped this way. The duplicated items need to be removed from the database level.