when Live plugin is disabled, do not show error in Segment value auto-suggest

Got: big red notification "The plugin Live is not enabled. You can activate the plugin on Settings > Plugins page in Piwik."

Expected: instead, simply do not show auto-suggest values and silently fail.

I tried to add this line to the Segmentation.js:594, but it didn't work:

```
   ajaxHandler.setErrorCallback(function () {});
```
