Testing for VIEWPANE=off

In a button this seems to be never true:

@if:Set VIEWPANE=off

Interestingly, inverting helps:

@if:!Set VIEWPANE=on

That works as expected.

A little demo:

// @if:!Set VIEWPANE=on
@if:Set VIEWPANE=off
Set VIEWPANE=on
@if:else
Set VIEWPANE=togglelayout

P.S.: Testing for Set DUAL=off works fine, e.g.

@if:Set DUAL=off
Set DUAL=on
@if:else
Set DUAL=togglelayout

Thanks! We'll fix that for 12.18.1.