Changes

esim.saip.ProfileElementUSIM: Fix IMSI decode if [only] template based

In case the fileDescriptor of EF.IMSI is purely template based and only
the file content is given in the actual profile, we must pass a template
reference to the File() constructor before we can read the IMSI.

This fixes the following exception for some profiles:
	ValueError: File(ef-imsi): No fileDescriptor found in tuple, and none set by template before

Change-Id: I14157a7b62ccd9b5b42de9b8060f2ebc5f91ebb3