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/traverse/lib/hub.js

@@ -0,0 +1,23 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.default = void 0;
+
+class Hub {
+  getCode() {}
+
+  getScope() {}
+
+  addHelper() {
+    throw new Error("Helpers are not supported by the default hub.");
+  }
+
+  buildError(node, msg, Error = TypeError) {
+    return new Error(msg);
+  }
+
+}
+
+exports.default = Hub;