Fix js error when no audio file present.

lute/templates/read/index.html

@@ -269,23 +269,19 @@ <h2>&#127881;</h2>
 
 <script>
   $(document).ready(function () {
-    show_player();
+    if (have_audio_file()) {
+      // Don't actually load the source -- for some reason,
+      // the ajax page load was causing the audio src to
+      // only load occasionally!  Not sure why.  Source loading
+      // is handled in load_player_source().
+      $('div.audio-player-container').show();
+    }
     goto_relative_page(0, true);
   });
 
-  /**
-   * If book_audio_file is not null, set up the player.
-   *
-   * Don't actually load the source -- for some reason,
-   * the ajax page load was causing the audio src to
-   * only load occasionally!  Not sure why.  Source loading
-   * is handled in load_player_source().
-   */
-  let show_player = function() {
-    const have_file = ($('#book_audio_file').val() != '');
-    if (have_file) {
-      $('div.audio-player-container').show();
-    }
+
+  let have_audio_file = function() {
+    return ($('#book_audio_file').val() != '');
   }
 
   /**
@@ -404,7 +400,7 @@ <h2>&#127881;</h2>
 
         // Magic hack for player source to load consistently
         // in Firefox.
-        if (load_source_file) {
+        if (load_source_file && have_audio_file()) {
           load_player_source();
         }
       }