pySim.esim.saip: Meaningful defaults in PE Constructor + test

Let's make sure the constructor of ProfileElement subclasses set
meaningful defaults to the self.decoded member, so that the to_der()
method can actually encode it.   This is required when constructing
a profile from scratch, as opposed to loading an existing one from DER.

Also, add a test to verify that the encoder passes without exception;
doesn't test the generated binary data.

Change-Id: I401bca16e58461333733877ec79102a5ae7fe410

tests/test_esim_saip.py

@@ -63,6 +63,17 @@ class SaipTest(unittest.TestCase):
         # TODO: we don't actually test the results here, but we just verify there is no exception
         pes.to_der()
 
+    def test_constructor_encode(self):
+        """Test that DER-encoding of PE created by "empty" constructor works without raising exception."""
+        for cls in [ProfileElementMF, ProfileElementPuk, ProfileElementPin, ProfileElementTelecom,
+                    ProfileElementUSIM, ProfileElementISIM]:
+            with self.subTest(cls.__name__):
+                pes = ProfileElementSequence()
+                inst = cls()
+                pes.append(inst)
+                pes.to_der()
+
+
 
 if __name__ == "__main__":
 	unittest.main()