fix: fix missing isMobile

Author: D-Sketon

layout/_partial/after-footer.ejs

@@ -325,7 +325,8 @@
     <script>
     var setupAPlayer = () => {
       if (!<%= theme.player.disable_on_mobile %> || !window.matchMedia('(max-width: 768px)').matches) {
-        if (window.matchMedia('(max-width: 959px)').matches) {
+        const isMobile = window.matchMedia('(max-width: 959px)').matches;
+        if (isMobile) {
           const aplayer = _$('#aplayer');
           if (aplayer) {
             const aside = aplayer.parentNode?.parentNode;