Bug 10277: (follow-up) if no userenv is set, act like a superlibrarian

Bug 10277: (follow-up) if no userenv is set, act like a superlibrarian

This patch fixes an error caught by t/db_dependent/Acquisition.t, and
adjusts C4::Context::IsSuperLibrarian() to return true if no
userenv is set. This is done on the basis that if no userenv is set,
calls to C4::Context routines are being made from a command-line script,
and if you have access to the command line of a running Koha instance,
you implicitly already have better than superlibrarian access.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>