bug#43703: 26.1: gpg window selection

[Boruch Baum]

When saving a file with a file-name extension `gpg', emacs intelligently
and helpfully opens an encryption dialog buffer in a separate window.
However, when the interaction with that buffer completes and emacs kills
the buffer, it does not switch focus back to the original window (that
of the foo.gpg file that was being edited / saved).

To recreate: Open a frame with two windows, find a file with extension
gpg, save it, follow instructions in the gpg window.

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