Fix override of --plain and --paging

[einfachIrgendwer0815]

Fixes #2731 while maintaining what #2660 tried to achieve.

That means the following combinations of --plain and --paging now work as expected:

bat <file> --plain --paging=never           # plain style, no paging
bat <file> --plain --plain --paging=always  # plain style, paging -> the second --plain gets overriden by --paging=always but not the first
bat <file> --paging=never --plain           # plain style, no paging

Fixes #2731
Fixes #3035

[keith-hall]

Thanks! :)