wincmd H/J/K/L doesn't respect 'winfixwidth' and 'winfixheight'

[tweekmonster]

Tested in 8.0.0344 and 7.4.1689.

For the problem with winfixheight, there has to already be two vertical windows. This is not an issue if there are only only horizontally stacked windows.

:vs
:split | resize 10 | set winfixheight | wincmd J
:split | resize 10 | set winfixheight | wincmd J

Screnshot: https://share.esdf.io/EWMaajBW9I/

In the case of winfixwidth, there are no prerequisites:

:vs | vertical resize 20 | set winfixwidth | wincmd L

The first time the above commands are run, the windows are equal widths. Repeating it creates smaller windows to the far right, but never the width I expected until there isn't enough room to spread them out.

Screenshot (after three runs): https://share.esdf.io/y9erLk1KaI/

[tweekmonster]

I think #931 may be related.