Prevent poll option from auto-deleting when text is cleared

[Ross-Sherlock]

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Description

Fixes #7608 - Prevents deletion of an empty poll option when the user is still editing the option. Achieved by row deletion logic from onChange to onBlur.

Please write a summary of your test approach:

• What kind of manual testing did you do?
  Manual testing
• Did you write any new tests?
  No
• What operating systems did you test with? (please use specific versions: http://whatsmyos.com/)
  macOS 10.15.7
• What other devices did you test with? (other Desktop devices, Android, Android Simulator, iOS, iOS Simulator)
  None