Not possible to revert the action of hiding all columns

[neolit123]

Describe the issue:

• Bug
• Change request
• New feature request
• Discussion request

Issue long description:

https://groups.google.com/d/msgid/subsurface-divelog/94c88054-724b-42fb-b762-79459c50852a%40googlegroups.com?utm_medium=email&utm_source=footer

I (foolishly) removed all the columns from the dive list (all the rows in the dive list had become shorter than normal after I had been rearranging columns and I couldn't find a way to change the height of the rows).

Having removed all the columns there seems to be no way to add them back - right click doesn't show a list of columns to be added.
I tried uninstall, clear the %appdata% folders, reinstall, but I got the same blank dive list :(

Operating system:

confirmed on Windows 7 and 10.

Subsurface version:

latest master

Steps to reproduce:

• right click the divelist header and uncheck all columns
• the divelist header with the columns is gone and columns cannot be shown any more

Current behavior:

the header with the columns is hidden if all columns are hidden

Expected behavior:

prevent the user from hiding all columns

Additional information:

PR is WIP.

Mentions: