Allow event's func to be async (#1461)

Fixes #1344.

telethon/events/raw.py

@@ -46,6 +46,8 @@ class Raw(EventBuilder):
         return update
 
     def filter(self, event):
-        if ((not self.types or isinstance(event, self.types))
-                and (not self.func or self.func(event))):
+        if not self.types or isinstance(event, self.types):
+            if self.func:
+                # Return the result of func directly as it may need to be awaited
+                return self.func(event)
             return event