Fixed issue #CT-614: exporting responses in "Full answers" mode does …

…not export the comment field of the "List with comment" question type

application/helpers/admin/export/SurveyObj.php

@@ -148,7 +148,7 @@ public function getFullAnswer($fieldName, $answerCode, Translator $translator, $
                 break;
 
             case Question::QT_O_LIST_WITH_COMMENT:   //DROPDOWN LIST WITH COMMENT
-                if (isset($answer)) {
+                if (!empty($answer)) {
                     //This is one of the dropdown list options.
                     $fullAnswer = $answer;
                 } else {