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/@babel/helper-function-name/README.md

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+# @babel/helper-function-name
+
+> Helper function to change the property 'name' of every function
+
+See our website [@babel/helper-function-name](https://babeljs.io/docs/en/next/babel-helper-function-name.html) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/helper-function-name
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/helper-function-name --dev
+```