notifications: Add safeties to prevent incorrect notifications.

de04f0ad67 changed now notifications recipients were calculated, in
a manner that caused them to be sent when they should not have been.
ac70a2d2e1 was supposed to resolve this, but appears to have been
insufficient, as all three of these cases have been observed to still
happen.

Add safety checks immediately before notification, until the
underlying logic error can be sussed out.

zerver/lib/push_notifications.py

@@ -896,6 +896,17 @@ def handle_push_notification(user_profile_id: int, missed_message: Dict[str, Any
         return
     user_profile = get_user_profile_by_id(user_profile_id)
 
+    if user_profile.is_bot:
+        # BUG: Investigate why it's possible to get here.
+        return  # nocoverage
+
+    if not (
+        user_profile.enable_offline_push_notifications
+        or user_profile.enable_online_push_notifications
+    ):
+        # BUG: Investigate why it's possible to get here.
+        return  # nocoverage
+
     try:
         (message, user_message) = access_message(user_profile, missed_message["message_id"])
     except JsonableError: