MDL-41635 Reports: Added missing string in loglive reports

Under course administration navigation log live doesn't appear
or appear with empty string (in some themes), this is happening
because text passed is empty.

report/loglive/lib.php

@@ -39,7 +39,7 @@ function report_loglive_extend_navigation_course($navigation, $course, $context)
     global $CFG, $OUTPUT;
     if (has_capability('report/loglive:view', $context)) {
         $url = new moodle_url('/report/loglive/index.php', array('id'=>$course->id, 'inpopup'=>1));
-        $action = new action_link($url, get_string('pluginname', 'report_loglive'), new popup_action('click', $url));
-        $navigation->add('', $action, navigation_node::TYPE_SETTING, null, null, new pix_icon('i/report', ''));
+        $action = new action_link($url, '', new popup_action('click', $url));
+        $navigation->add(get_string('pluginname', 'report_loglive'), $action, navigation_node::TYPE_SETTING, null, null, new pix_icon('i/report', ''));
     }
 }