Stop user directory from failing if it encounters users not in the users table. (#11053)

The following scenarios would halt the user directory updater:

- user joins room
- user leaves room
- user present in room which switches from private to public, or vice versa.

for two classes of users:

- appservice senders
- users missing from the user table.

If this happened, the user directory would be stuck, unable to make forward progress.

Exclude both cases from the user directory, so that we ignore them.

Co-authored-by: Eric Eastwood <erice@element.io>
Co-authored-by: reivilibre <oliverw@matrix.org>
Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>
Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

synapse/logging/opentracing.py

@@ -807,6 +807,14 @@ def trace(func=None, opname=None):
                         result.addCallbacks(call_back, err_back)
 
                     else:
+                        if inspect.isawaitable(result):
+                            logger.error(
+                                "@trace may not have wrapped %s correctly! "
+                                "The function is not async but returned a %s.",
+                                func.__qualname__,
+                                type(result).__name__,
+                            )
+
                         scope.__exit__(None, None, None)
 
                     return result