chore($parse): micro-optimization for ensureSafeObject function
chore($parse): micro-optimization for ensureSafeObject function

This version matches the "alternate 2.2" version here: http://jsperf.com/ensuresafeobject/2

alternate 2.3 is a bit faster and simpler, but would break backwards compatibility.

Closes #5246

ammula88/angular.js,ammula88/angular.js,ammula88/angular.js,ammula88/angular.js,ammula88/angular.js