wayland/actor-surface: Always consider unmapped actors not on output

This avoids using bogus geometric values from an unmapped actor to
determine whether an actor is on a logical monitor or not. This would
happen when committing to a subsurface of a yet to be mapped toplevel.

!961
4 jobs for master in 7 minutes and 11 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #550841
build-mutter

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passed #550842
build-without-native-backend-and-wayland

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  Test
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can-build-gnome-shell

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passed #550843
test-mutter

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