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/@jest/source-map/build/index.js

@@ -0,0 +1,25 @@
+'use strict';
+
+Object.defineProperty(exports, '__esModule', {
+  value: true
+});
+Object.defineProperty(exports, 'getCallsite', {
+  enumerable: true,
+  get: function get() {
+    return _getCallsite.default;
+  }
+});
+Object.defineProperty(exports, 'SourceMapRegistry', {
+  enumerable: true,
+  get: function get() {
+    return _types.SourceMapRegistry;
+  }
+});
+
+var _getCallsite = _interopRequireDefault(require('./getCallsite'));
+
+var _types = require('./types');
+
+function _interopRequireDefault(obj) {
+  return obj && obj.__esModule ? obj : {default: obj};
+}