Android. Banana Split. Import wrong mnemonic lead to broken key set on device.

[stepanLav]

When user import key set via Banana Split - https://bs.parity.io/#/
key set will be created, but without any keys and secrets. That lead to a problem when user can't delete this data.

Case:

1. Create wrong mnemonic Banana Split
2. Try to import it

Expected result:
Wrong mnemonics will not be imported, key set will not be created

Actual result:
Key set will be created, but mnemonic will be empty, which results to broken key set. Such key set cannot be selected or deleted. Only wipe all data can remove it.

Test data:

Example case:

Untitled.mp4

Environment:
Android app v6.3.1