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/_initCloneObject.js

@@ -0,0 +1,18 @@
+var baseCreate = require('./_baseCreate'),
+    getPrototype = require('./_getPrototype'),
+    isPrototype = require('./_isPrototype');
+
+/**
+ * Initializes an object clone.
+ *
+ * @private
+ * @param {Object} object The object to clone.
+ * @returns {Object} Returns the initialized clone.
+ */
+function initCloneObject(object) {
+  return (typeof object.constructor == 'function' && !isPrototype(object))
+    ? baseCreate(getPrototype(object))
+    : {};
+}
+
+module.exports = initCloneObject;