Stubs generation doesn't correctly stop when encountering errors

[cursive-ide]

If the stub generation produces an error, occasionally Cursive doesn't catch the error correctly. Additionally, if the user has automatic stub generation enabled, this will cause the generation to loop indefinitely.

1. Ensure that the current error case (data_readers conflict) is caught.
2. When errors occur during the stub generation, turn off automatic generation. This will cause the notification to be shown when generation is next required, and the user can opt to turn it back on then.