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/_customOmitClone.js

@@ -0,0 +1,16 @@
+var isPlainObject = require('./isPlainObject');
+
+/**
+ * Used by `_.omit` to customize its `_.cloneDeep` use to only clone plain
+ * objects.
+ *
+ * @private
+ * @param {*} value The value to inspect.
+ * @param {string} key The key of the property to inspect.
+ * @returns {*} Returns the uncloned value or `undefined` to defer cloning to `_.cloneDeep`.
+ */
+function customOmitClone(value) {
+  return isPlainObject(value) ? undefined : value;
+}
+
+module.exports = customOmitClone;