Bug 11587: get rid of warnings generated by IsSuperLibrarian with anonymous sessions

Bug 11587: get rid of warnings generated by IsSuperLibrarian with anonymous sessions

This corrects line 1250 of C4/Context.pm to be:
    return ($userenv->{flags}//0) % 2;
And thus avoids an uninitialized value used in the modulus.

TEST PLAN
---------
1) Apply the first patch (to update t/Context.t)
2) prove -v t/Context.t
-- This should fail tests 7 and 8
3) Apply this patch (to fix C4/Context.pm)
4) prove -v t/Context.t
-- All tests should succeed

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>