display: Fix Apply button showing for changes to disabled monitor

Disabled monitors may or may not have a mode selected. This means, we
need to skip the mode comparison if the two compared monitors are
disabled (i.e. have no logical monitor).
Move the mode check to the end and skip it if both monitors are disabled.

This fixes cases where identical configurations are misdetected, because
we applied a mode to a monitor and disabled the monitor again. This
happens for example when switching the active monitor in "single" mode.
11 jobs for benzea/fix-single-display-405 in 2 minutes and 55 seconds (queued for 4 seconds)
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