mi: Shortcut miDoCopy/miCopyArea based on clipList

This is maybe one more comparison, but it catches FullyObscured windows
slightly earlier, so it's kind of a wash. The important thing is this
allows for paintable but unmapped windows, which will have non-empty
3 jobs for pre-bsa-cleanups in 13 minutes and 22 seconds (queued for 13 minutes and 16 seconds)