ui: Make sure right trim doesn't try to overtrim (#8171)

ui-v2/app/utils/right-trim.js

@@ -1,4 +1,7 @@
 export default function rightTrim(str = '', search = '') {
   const pos = str.length - search.length;
+  if (pos >= 0) {
     return str.lastIndexOf(search) === pos ? str.substr(0, pos) : str;
+  }
+  return str;
 }

ui-v2/tests/unit/utils/right-trim-test.js

@@ -37,6 +37,22 @@ module('Unit | Utility | right trim', function() {
         args: ['/a/folder/here/', '/a/folder/here/'],
         expected: '',
       },
+      {
+        args: ['/a/folder/here/', '-'],
+        expected: '/a/folder/here/',
+      },
+      {
+        args: ['/a/folder/here/', 'here'],
+        expected: '/a/folder/here/',
+      },
+      {
+        args: ['here', '/here'],
+        expected: 'here',
+      },
+      {
+        args: ['/here', '/here'],
+        expected: '',
+      },
     ].forEach(function(item) {
       const actual = rightTrim(...item.args);
       assert.equal(actual, item.expected);