Added check for msgpack strings in case LXMF client sent that for their name

LXMF/LXMF.py

@@ -115,6 +115,9 @@ def display_name_from_app_data(app_data=None):
                     if dn == None:
                         return None
                     else:
+                        # if it was packed as a string, then we don't need to decode it
+                        if isinstance(dn, str):
+                            return dn
                         try:
                             decoded = dn.decode("utf-8")
                             return decoded