MFC r326526:

In case man(1) found a catpage to display skip looking ".so" which is manpage
only.

In case we are trying to read a catpage, the manpage variable is not defined.
It results in the "cattool" having no arguments.

In case the catpage is compressed, the cattool used is "zcat" which dies if the
standard input is a terminal, meaning the function calling it is exiting as if
there were no ".so"
In case the catpage is uncompressed, the cattool used is "zcat -f" which waits
reading standard input, making the man(1) command hang.

PR: 223560
Reported by: wosch