`TextArea` cannot `addText` if `TextArea` is already visibly filled
```nim
  procProcess(filePaths).apply(
    proc (x: string) =
      textArea.addText(x)
      textArea.addText(longLineBreak)
  )
```

Actions like these only work, if the `TextArea` is not "full" from the user's perspective. If the whole area is "filled" with characters, then no additional text will be appended, to be viewable by scrolling.
Appending text only works as long as there is still space in the `TextArea`.

It's not like #89, though. The first time something is added, the text can make the `TextArea` scrollable and therefore add text beyond the visible area. However, if you then try to append further text, it simply won't happen.

Platform: Windows