iOS: fix selectValue for iOS8

git-svn-id: https://geuz.org/svn/gmsh/trunk@19953 59c8cabf-10d6-4a28-b43f-3936b85956c4
git-svn-id: https://geuz.org/svn/gmsh/trunk@19954 59c8cabf-10d6-4a28-b43f-3936b85956c4