[NcAppContent] pane resize broken with 9.0.0-rc.1

[wofferl]

Using 9.0.0-rc.1 in the Nextcloud News App throws following error, when using split mode and the position is not stored in the browser store.

13:11:05.240 Uncaught (in promise) TypeError: e[0] is undefined
    handlePaneResize NcUserStatusIcon-M_93a-z6.mjs:8
    kn _l10n-dinIMiE_.mjs:47
    It _l10n-dinIMiE_.mjs:47
    aD _l10n-dinIMiE_.mjs:55
    Ze NcUserStatusIcon-M_93a-z6.mjs:8
    Q NcUserStatusIcon-M_93a-z6.mjs:8
    X NcUserStatusIcon-M_93a-z6.mjs:8
    P NcUserStatusIcon-M_93a-z6.mjs:8
    onmousedown NcUserStatusIcon-M_93a-z6.mjs:8
NcUserStatusIcon-M_93a-z6.mjs:8:18

This is also reproducible on the Nextcloud Vue Style Guide when using the slider in the following demo

13:09:10.485 Uncaught TypeError: t[0] is undefined
    handlePaneResize https://nextcloud-vue-components.netlify.app/build/bundle.e4e93fb1.js:2
    Nn https://nextcloud-vue-components.netlify.app/build/bundle.e4e93fb1.js:2
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bundle.e4e93fb1.js:2:4348744