get_config / unit tests MDL-24977 get_config('a_plugin'); should return something false when there is no config.

It was always casting the result to an object, even when it was an empty array. I changed it to return null in this case. So that if (get_config('a_plugin')) { /* Do something relying on the pugin having config */ ) works.

lib/moodlelib.php

@@ -1046,7 +1046,11 @@ function get_config($plugin, $name = NULL) {
                 }
             }
         }
-        return (object)$localcfg;
+        if ($localcfg) {
+            return (object)$localcfg;
+        } else {
+            return null;
+        }
 
     } else {
         // this part is not really used any more, but anyway...