Fix bstats perms chart when using an unsupported permissions plugin

Author: lorenzop

Essentials/src/main/java/com/earth2me/essentials/perm/impl/SuperpermsHandler.java

@@ -170,6 +170,8 @@ public String getEnabledPermsPlugin() {
                 break;
             }
         }
+        if (enabledPermsPlugin == null)
+            enabledPermsPlugin = "other";
         return enabledPermsPlugin;
     }
 }