Beware of SUBSURAFACES (sounds latin)

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56138 954f8c5b-7b00-dc11-b283-0030488c597c
Fix for #35015, Alpha input in color selectors was showing 0 precision. Probably caused by r55910. The NUMSLI button now needs either -1 or an explicit precision value in a2.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56139 954f8c5b-7b00-dc11-b283-0030488c597c