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

pySim/esim/saip/__init__.py

@@ -1130,7 +1130,8 @@ class ProfileElementUSIM(FsProfileElement):
 
     @property
     def imsi(self) -> Optional[str]:
-        f = File('ef-imsi', self.decoded['ef-imsi'])
+        template = templates.ProfileTemplateRegistry.get_by_oid(self.templateID)
+        f = File('ef-imsi', self.decoded['ef-imsi'], template.files_by_pename.get('ef-imsi', None))
         return dec_imsi(b2h(f.body))
 
 class ProfileElementOptUSIM(FsProfileElement):