Use SWS_FULL_CHR_H_INT for SWS context for more accurate conversion

Suggestion by Bjeorn Sonnenschein from report #34755.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55956 954f8c5b-7b00-dc11-b283-0030488c597c