In commit 7e1f86d4 monitor support was added to randr. At this time it seemed to be reasonable not to have
more than one (virtual) monitor on a particular physical display. The code was never changed since.
Nowadays, extremely large displays exists (4k displays, ultra-wide displays). In some use cases it makes sense to
split these large physical displays into multiple virtual monitors. An example are ultra-wide screens that can be
split into 2 monitors. The change in this commit makes this work.
Besides that, removing a monitor in a function that is called "RRMonitorAdd" is bad practice and causes
unexpected behaviour.
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