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/cache.js

@@ -0,0 +1,26 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.clear = clear;
+exports.clearPath = clearPath;
+exports.clearScope = clearScope;
+exports.scope = exports.path = void 0;
+let path = new WeakMap();
+exports.path = path;
+let scope = new WeakMap();
+exports.scope = scope;
+
+function clear() {
+  clearPath();
+  clearScope();
+}
+
+function clearPath() {
+  exports.path = path = new WeakMap();
+}
+
+function clearScope() {
+  exports.scope = scope = new WeakMap();
+}