filesystem: Introduce support for TLV parser

This adds an easy way for files to make use of the pySim.tlv parser.

All a file has to do is to specify a _tlv member which points to
either a TLV_IE or a TLV_IE_Collection instance.

Change-Id: I59f456b4223ec88081e91cee168b654c69bcb5f4

pySim/tlv.py

@@ -338,6 +338,8 @@ class TLV_IE_Collection(metaclass=TlvCollectionMeta):
         while len(remainder):
             # obtain the tag at the start of the remainder
             tag, r = first._parse_tag_raw(remainder)
+            if tag == None:
+                return res
             if tag in self.members_by_tag:
                 cls = self.members_by_tag[tag]
                 # create an instance and parse accordingly