Undefined index: download in distro_update_rebuild_make_data

A child distribution (e.g. a distribution built on top of Panopoly) contains patch information in a .make file for a module defined in the parent distribution, then an undefined index notice is thrown when attempting to build the .make file information. This is a valid scenario if a distribution wants to include additional patches to a contrib that do not exist in the parent distribution.

This function is attempting to build the version information based on the ['version'] or ['download'][branch'] information in the .make file but doesn't check to make sure either exists before trying to grab the data. Need to add a condition in the foreach to continue if neither are found.