tabline: AirlineSelectTab still wrong sometimes
tabline: AirlineSelectTab still wrong sometimes

Partly revert commit 105e9daaf71d1493cdf342a2cc736cbb5
and fix #1857 another way, by making sure, that buffers are not taking
away from the s:current_visible_buffers list.

Fixes #1857
Fixes #1872

rchicoli/vim-airline,chrisbra/vim-airline,bling/vim-airline,yzhou61/vim-airline