Prevent accessing list index when no device is available also in _store_device_ids

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

slixmpp_omemo/__init__.py

@@ -286,6 +286,7 @@ class XEP_0384(BasePlugin):
         """Store Device list"""
         device_ids = []  # type: List[int]
         items = list(items)
+        if items:
             device_ids = [int(d['id']) for d in items[0]['devices']]
         return self._omemo.newDeviceList(str(jid), device_ids)