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/lodash/_baseForOwnRight.js

@@ -0,0 +1,16 @@
+var baseForRight = require('./_baseForRight'),
+    keys = require('./keys');
+
+/**
+ * The base implementation of `_.forOwnRight` without support for iteratee shorthands.
+ *
+ * @private
+ * @param {Object} object The object to iterate over.
+ * @param {Function} iteratee The function invoked per iteration.
+ * @returns {Object} Returns `object`.
+ */
+function baseForOwnRight(object, iteratee) {
+  return object && baseForRight(object, iteratee, keys);
+}
+
+module.exports = baseForOwnRight;