fix(protractor): throw index-out-of-bounds

See #915
- to make error more specific instead of propagate later

Author: hankduan

lib/protractor.js

@@ -584,6 +584,12 @@ var buildElementHelper = function(ptor) {
         // -1 is special and means last
         index = arr.length - 1;
       }
+
+      if (index >= arr.length) {
+        throw new Error('Index out of bound. Trying to access index:' + index + 
+            ', but locator: ' + locatorMessage + ' only has ' + 
+            arr.length + ' elements');
+      }
       return arr[index];
     });
     return new webdriver.WebElement(ptor.driver, id);