add no question focus option in submission navigation

now the default navigation has no question focus,
meaning that `Tab` does not skip other questions.
Initial cursor focus remains on question 1
even when no question filter is selected

submissions/static/submissions/detail.js

@@ -150,11 +150,13 @@ async function handleScroll () {
         console.log(`focusing on input[data-position="${initialFocusQuestionIndex}"]`);
 
         // remove tabindex from all other grade inputs
-        grade_inputs.forEach((input, i) => {
-            if (i !== initialFocusQuestionIndex) {
-                input.setAttribute("tabindex", "-1");
-            }
-        });
+        if (hasInitialFocusQuestionIndex) {
+            grade_inputs.forEach((input, i) => {
+                if (i !== initialFocusQuestionIndex) {
+                    input.setAttribute("tabindex", "-1");
+                }
+            });
+        }
     } else {
         const firstGradeInput = document.querySelector(`input[data-position="0"]`);
         console.log(`Failed. Focusing on first grade input because input[data-position="${initialFocusQuestionIndex}"] does not exist`);
@@ -481,11 +483,13 @@ if (pk === firstPk) {
 
 // try to get the initial focus question index from the url question_focus parameter
 let initialFocusQuestionIndex = 0;
+let hasInitialFocusQuestionIndex = false;
 try {
     const urlParams = new URLSearchParams(location.search);
     const questionFocus = urlParams.get("question_focus");
     if (questionFocus) {
         initialFocusQuestionIndex = parseInt(questionFocus);
+        hasInitialFocusQuestionIndex = true;
     }
 } catch (error) {
     console.log(`No question_focus parameter in url`);

submissions/templates/submissions/detail.html

@@ -670,13 +670,11 @@ <h5 class="mt-5">Set navigation filters</h5>
                 <label class="mt-3" for="id_filter_question" style="font-size:20px;">Focus on Question</label>
                 <div class="mt-2">
                     <select class="form-control selectpicker show-tick" data-show-subtext="true" title="Select question" data-live-search="true" name="filter_question" id="id_filter_question">
-                        {% comment %} <option data-hidden="true" value=""></option> {% endcomment %}
+                        <option value="">No filter</option>
                         {% with ''|center:submission.assignment.number_of_questions as range %}
                             {% for i in range %}
                             <option value="{{ forloop.counter0 }}"
-                                {% if forloop.counter0 == 0 and query_params.question_focus is None %}
-                                    selected
-                                {% elif forloop.counter0|slugify in query_params.question_focus|slugify %}
+                                {% if forloop.counter0|slugify in query_params.question_focus|slugify %}
                                     selected
                                 {% endif %}