Missing sender id in reactions panel when user has no display name

**Describe the bug**
Display bug:

In the reactions summary panel: reactions sent by user with no display name do not display any identification of the sender.

A participant who suppressed their display name (and profile pic) has sent a reaction to a message. While checking the senders of that message’s reactions, those that were sent by this user do not give any identification about the sender (blank space).

**To Reproduce**
Steps to reproduce the behavior:
1. Void out an account’s display name
2. React (emoji) to a message in room
3. Long press the reactions line or select message, ..., reactions; reactions summary panel opens
4. Reaction is visible but no name: neither display name — which doesn’t exist — nor mxid is visible.

**Expected behavior**
Reaction summary should fall back to mixd when no display name exists for an account that sent a reaction

**Screenshots**

https://matrix.to/#/!pMBteVpcoJRdCJxDmn%3Amatrix.org/%24qpvwLIi3AVUJR5rvjqM7a307zr46NW2s12mMBk8U3sQ

(Can’t figure out how to embed the pic from safari mobile)

**Smartphone (please complete the following information):**
- Device: iPhone SE v1
- OS: 14.4.2
- Browser stock browser, safari
- Version element 1.2.7

Start by reproducing the issue in the reactions summary panel after removing an account's display name, then trace the sender identification rendering from that panel. Done means reactions from accounts without display names show the sender's Matrix ID instead of a blank space.

Written by the indexing model from the issue text.