Fix bugs to pass Ruby unit tests

Author: jasonpaulos

npm_and_yarn/helpers/lib/npm/vulnerability-auditor.js

@@ -227,29 +227,21 @@ function groupBy(elems, fn) {
  * ArboristNode.location and will be of the form "node_modules/foo/node_modules/bar".
  */
 function lookupChildLocation(root, location) {
-  const parts = location.split('/');
-  let current = root;
-  let state = '';
+  if (!location.startsWith('node_modules/')) {
+    // The location must start with 'node_modules/' to be valid.
+    return null;
+  }
+  const parts = location
+    .substring('node_modules/'.length)
+    .split('/node_modules/')
+  let current = root
   for (const part of parts) {
-    if (state == '') {
-      if (part === 'node_modules') {
-        state = 'node_modules';
-      } else {
-        // Unexpected part
-        return null;
-      }
-    } else if (state === 'node_modules') {
-      state = '';
-      current = current.children.get(part);
-      if (!current) {
-        return null;
-      }
-    } else {
-      // Unexpected state
-      return null;
+    current = current.children.get(part)
+    if (!current) {
+      return null
     }
   }
-  return current;
+  return current
 }
 
 async function loadNpmConfig() {