language pack lost after update

When using the automatic updater to go from TB 4.0-alpha-2 to 4.0-alpha-3 the language pack extension seems to be lost.

Tested with the 4.0-alpha-2 es-ES build and MAR files from https://people.torproject.org/~mikeperry/builds/4.0-alpha-3/

My guess is that the MAR file was not created correctly. I will investigate.