Exception when editing date cell

[bmblb]

Reported here: https://www.bryntum.com/forum/viewtopic.php?f=43&t=14816

Steps to reproduce on cellEdit demo:

1. configure feature like this: cellEdit : { triggerEvent: 'cellclick' }
2. edit date cell, change value
3. click next cell
   Exception thrown:

CellEdit.js:431 Uncaught (in promise) TypeError: Cannot set property 'value' of null
    at CellEdit.onEditorComplete (CellEdit.js:431)
    at Editor.trigger (Events.js:842)
    at Editor.onEditComplete (Editor.js:515)
    at Editor.completeEdit (Editor.js:431)
    at async CellEdit.finishEditing (CellEdit.js:728)

[bmblb]

Related issue: #963