Fix contest submission querying.

modules/submission.js

@@ -47,7 +47,7 @@ app.get('/submissions', async (req, res) => {
     if (user) where.user_id = user.id;
     else if (req.query.submitter) where.user_id = -1;
 
-    if (req.query.contest == null) {
+    if (!req.query.contest) {
       where.type = { $ne: 1 };
     } else {
       const contestId = Number(req.query.contest);

views/submissions.ejs

@@ -15,6 +15,7 @@
   <% } %>
 
   <form action="<%= syzoj.utils.makeUrl(displayConfig.inContest ? ['contest', contest.id, 'submissions'] : ['submissions']) %>" class="ui mini form" method="get" role="form" id="form">
+    <input type="hidden" name="contest" value="<%= form.contest %>" />
     <div class="inline fields" style="margin-bottom: 25px; white-space: nowrap; ">
       <label style="font-size: 1.2em; margin-right: 1px; ">题目：</label>
       <div class="field"><input name="problem_id" style="width: 50px; " type="text" value="<%= form.problem_id %>"></div>