MDL-57757 mod_lesson: Handle empty answers

This is and edge case created by a bug in the numeric question type.

mod/lesson/classes/external.php

@@ -1860,8 +1860,10 @@ class mod_lesson_external extends external_api {
                                     'response' => new external_value(PARAM_RAW, 'The response text.'),
                                     'responseformat' => new external_format_value('response.'),
                                     'answers' => new external_multiple_structure(
-                                        new external_multiple_structure(new external_value(PARAM_RAW, 'Possible answers and info.'))
-                                    )
+                                        new external_multiple_structure(new external_value(PARAM_RAW, 'Possible answers and info.')),
+                                        'User answers',
+                                        VALUE_OPTIONAL
+                                    ),
                                 ), 'Answer data (empty in content pages created in Moodle 1.x).', VALUE_OPTIONAL
                             )
                         )

mod/lesson/report.php

@@ -328,7 +328,7 @@ if ($action === 'delete') {
         $table->data[] = array($fontstart.get_string("question", "lesson").": <br />".$fontend.$fontstart2.$page->contents.$fontend2, " ");
         $table->data[] = array($fontstart.get_string("answer", "lesson").":".$fontend, ' ');
         // apply the font to each answer
-        if (!empty($page->answerdata)) {
+        if (!empty($page->answerdata->answers)) {
             foreach ($page->answerdata->answers as $answer){
                 $modified = array();
                 foreach ($answer as $single) {