MDL-74808 question: only add title attr if tooltip is set

lib/templates/single_button.mustache

@@ -58,7 +58,7 @@
         {{/params}}
         <button type="submit" class="btn {{#primary}}btn-primary{{/primary}}{{^primary}}btn-secondary{{/primary}}"
             id="{{id}}"
-            title="{{tooltip}}"
+            {{#tooltip}}title="{{tooltip}}"{{/tooltip}}
             {{#disabled}}disabled{{/disabled}}
             {{#attributes}} {{name}}="{{value}}" {{/attributes}}>{{label}}</button>
     </form>

question/bank/editquestion/classes/editquestion_helper.php

@@ -78,9 +78,13 @@ class editquestion_helper {
         if ($canadd) {
             $params['category'] = $categoryid;
             $url = new \moodle_url('/question/bank/editquestion/addquestion.php', $params);
+            $buttonparams = ['disabled' => $disabled];
+            if (!empty($tooltip)) {
+                $buttonparams['title'] = $tooltip;
+            }
             $addquestiondisplay['buttonhtml'] = $OUTPUT->single_button($url,
                     get_string('createnewquestion', 'question'),
-                    'get', array('disabled' => $disabled, 'title' => $tooltip));
+                    'get', $buttonparams);
             $addquestiondisplay['qtypeform'] = self::print_choose_qtype_to_add_form(array());
         }
         return $PAGE->get_renderer('qbank_editquestion')->render_create_new_question_button($addquestiondisplay);