don't reexpand sidepanels if they were explicitly hidden

[matrixbot]

Created by @ matthew:matrix.org.

[grahamperrin]

Thanks @t3chguy for directing me to this issue. https://matrix.to/#/!DgvjtOljKujDBrxyHk:matrix.org/$1494076559782751aeJmQ:matrix.org today I wrote:

I recently read a comment complaining that the right hand sidebar is no longer automatically disclosed when a window is resized.

– or words to that effect.

Funny, because I find that automation annoying :-)

When I actively close something, I want it to be closed.

Found: #1371 (comment) @sbts

[t3chguy]

dup #659