Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/uri-js/dist/esnext/schemes/https.js

@@ -0,0 +1,9 @@
+import http from "./http";
+const handler = {
+    scheme: "https",
+    domainHost: http.domainHost,
+    parse: http.parse,
+    serialize: http.serialize
+};
+export default handler;
+//# sourceMappingURL=https.js.map