Kasumi crashes if one tries to save with empty fields

[DarkTrick]

Description
===========
If there is a row with `Spelling` OR `Sound` empty, Kasumi crashes on saving and looses all previously unsaved data.

Reproduce
==========
- Open `kasumi`
- Press button `Add`
- Press button `Save`

Actual
------
Kasumi crashes, all unsaved data is lost (i.e. previous entries within that 'session', that should've been saved with that last click).

Expected:
---------
- Kasumi saves all entries, that are savable.
- Kasumi does not crash.

- Maybe: An error message.
- Maybe: Mark the erroneous file light red.

lsb_release -rd
================
Description: Ubuntu 20.10
Release: 20.10

apt-cache policy kasumi
========================
kasumi:
  Installed: 2.5-9build1
  Candidate: 2.5-9build1
  Version table:
 *** 2.5-9build1 500
        500 http://archive.ubuntu.com/ubuntu groovy/universe amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 20.10
Package: kasumi 2.5-9build1
ProcVersionSignature: Ubuntu 5.8.0-34.37-generic 5.8.18
Uname: Linux 5.8.0-34-generic x86_64
ApportVersion: 2.20.11-0ubuntu50.3
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Tue Jan 5 22:08:19 2021
SourcePackage: kasumi
UpgradeStatus: No upgrade log present (probably fresh install)