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/debug/src/inspector-log.js

@@ -0,0 +1,15 @@
+module.exports = inspectorLog;
+
+// black hole
+const nullStream = new (require('stream').Writable)();
+nullStream._write = () => {};
+
+/**
+ * Outputs a `console.log()` to the Node.js Inspector console *only*.
+ */
+function inspectorLog() {
+  const stdout = console._stdout;
+  console._stdout = nullStream;
+  console.log.apply(console, arguments);
+  console._stdout = stdout;
+}