Fix Coverty Scan ID 1342042 - Explicit null dereferenced
Review Request #127958 - Created May 18, 2016 and submitted
KGameThemeSelectorPrivate::_k_updateThemeList() was made more robust to
prevent null pointer access when an entry in themeMap was not found.
For this case the value() method returns a null pointer which was not
checked before refactoring.