fix #401 mandrillaImage being reversed

Reversing the image if axis is invisible is not needed.
Manual test with R2011b and R2014b by commenting out `axis off` in test case.
Removed black background to allow visual control, if axis is really of.
Merge pull request #420 from PeterPablo/fix_#401_ACID_mandrillaImage

fix #401 mandrillaImage being reversed