pacmacs--normalize-wall-bits is not UT covered completely

[rexim]

Even though it should be.

Here is the UT:

pacmacs.el/test/pacmacs-image-test.el

Line 90 in 769414f

(ert-deftest pacmacs--normalize-wall-bits-test ()

And here is its coverage: https://coveralls.io/builds/4101407/source?filename=pacmacs-image.el#L85