Don't push childViews if undefined/invalid (issue #2967)

Since 3a16e2821d021a2c88ac290516825ca3b0cafa62, pushObjects throws an error when provided with null or undefined.

Checking the childViews property for compatibility with the pushObjects method prior to calling pushObjects. Will not attempt to push invalid objects.
Simplified to existence check

As suggested by @stefanpenner
Merge pull request #2975 from realityendshere/fix-childview-pushobjects

Don't push childViews if undefined/invalid (issue #2967)