Fix reflow on resize when in alternate buffer.

Summary:
After commit 05d091483a29e7937914e9fd4e94d0c6d9043aad screen swap form
alternate buffer to primary buffer is not the same as the reversed. Take this
into account when resizing.

Test Plan: Build history, man echo, resize, quit manual.

Reviewers: billiob

Differential Revision: https://phab.enlightenment.org/D370