shell-no-trail-bslash: improve diagnostic in case of failure * t/ax/shell-no-trail-bslash.in: Here, by fixing a typo in a variable name and a logic error. * t/self-check-shell-no-trail-bslash.sh: Enhance to catch the issue. Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>