Do not attempt to sort themes when themes are disabled (bug #1243883).

libraries/select_theme.lib.php

@@ -75,10 +75,9 @@ if ($PMA_ThemeAvailable == TRUE) { // themeManager is available
         } // end get themes
     } // end check for themes directory
     closedir($handleThemes);
+    asort($available_themes_choices);
 } // end themeManger
 
-asort($available_themes_choices);
-
 // Allow different theme per server
 $theme_cookie_name = 'pma_theme';
 if ($GLOBALS['cfg']['ThemePerServer']) {