Having a poll as a root event causes multiple problems

### Steps to reproduce

1. Where are you starting? What can you see?
-A user has started a poll in an encrypted room
-Another user starts a thread from that poll
2. What do you click?
-I get a system notification for the threaded reply
3. More steps…
-I tap the notification and land in that thread

### Outcome

#### What did you expect?
I expected to see the poll on the top of the thread and the reply underneath it.
#### What happened instead?
The reply was rendered above the actual root event.

Screenshot:

After that, I went back to that room's timeline and it showed "Encrypted message" in every thread summary:

I tried restarting the app and going into the room. Each time I would scroll to the end, I'd get a screen with only the poll showing. If I tapped on "Jump to unread" I'd get back to timeline. Here's a video:

https://user-images.githubusercontent.com/18530109/161769079-933e61b6-42f8-4b42-808d-23c5e1f9dd28.mp4

I wanted to submit a rageshake but couldn't, due to #5985

### Your phone model

iPhone 11 Pro

### Operating system version

iOS 15.4.1

### Application version

1.8.11 (20220404113509)

### Homeserver

matrix.org

### Will you send logs?

No

Start by reproducing the issue from a notification into a thread whose root event is a poll in an encrypted room on iOS. Verify that the poll appears above its reply, thread summaries do not show "Encrypted message," and scrolling to the end does not leave only the poll visible.

Written by the indexing model from the issue text.