Update score.js for records no longer in music_db (#3)

Quick guard matching other functions to stop getReleaseDate() from failing

sdvx@asphyxia/webui/asset/js/score.js

@@ -20,6 +20,9 @@ function getReleaseDate(musicid) {
     //console.log(music_db["mdb"]["music"])
     //console.log(musicid+" "+type);
     var result = music_db["mdb"]["music"].filter(object => object["@id"] == musicid);
+    if (result.length == 0) {
+        return "Unknown";
+    }
     return result[0]["info"]["distribution_date"]["#text"]
         //console.log(result);
 }
@@ -286,4 +289,4 @@ $(document).ready(function() {
     });
 
 
-})
+})