fix(bar): normalise onOtherMonitor to bool (#2050)

* fix(bar): normalise onOtherMonitor to bool

`onOtherMonitor` is a bool property but returns the monitor object when the
workspace is unoccupied, since showUnoccupied (default true) displays workspaces
that do not exist yet. This warns 'Unable to assign [undefined] to bool' and
makes off-monitor dimming silently not apply with perMonitor: false.

Closes #2049.

* Update modules/bar/components/workspaces/Workspace.qml

Co-authored-by: Danny Atropos <danny@atropos.cc>

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Co-authored-by: 2 * r + 2 * t <61896496+soramanew@users.noreply.github.com>
Co-authored-by: Danny Atropos <danny@atropos.cc>