Ensure expect_problems is a dict within encrypt_message

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

slixmpp_omemo/__init__.py

@@ -579,7 +579,9 @@ class XEP_0384(BasePlugin):
             # or if we hit the same set of errors.
             errors = []  # type: List[omemo.exceptions.OMEMOException]
 
-            if expect_problems is not None:
+            if expect_problems is None:
+                expect_problems = {}
+
             expect_problems = {jid.bare: did for (jid, did) in expect_problems.items()}
 
             try: