fix for 0004528: [localization] Error on logout page with language=auto
added admin check for $g_fallback_language not 'auto'

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2980 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9