'eventStreams' is either undefined, null or an Array. So check for truth...

...iness

before trying to use it like an Array. Fixes #3319 for the branch. This is
probably not a fully correct fix.

@shane-tomlinson - if you have a different way you'd like to fix this, please do :-). This PR has a code smell. 

Note: this PR is for the train-2013.04.26 branch.