Improve behavior of calling reply command when point is on username using "Elemental" message format

To reproduce:
1. Open the room list
2. Enter a room
3. Attempt to use `S-RET` or `M-x ement-room-write-reply` to reply to a message point

This fails with the following trace:
```lisp
Debugger entered--Lisp error: (cl-assertion-failed ((ement-event-p (ewoc-data (ewoc-locate ement-ewoc))) nil))
cl--assertion-failed((ement-event-p (ewoc-data (ewoc-locate ement-ewoc))))
ement-room-write-reply()
#(ement-room-write-reply)
apply(# ement-room-write-reply)
funcall-interactively(ement-room-write-reply)
#(ement-room-write-reply nil nil)
apply(# (ement-room-write-reply nil nil))
explain-pause--wrap-call-interactively(# ement-room-write-reply nil nil)
apply(explain-pause--wrap-call-interactively # (ement-room-write-reply nil nil))
call-interactively(ement-room-write-reply nil nil)
command-execute(ement-room-write-reply)
```
Specifically, I am using Nix's `emacs29-pgtk` [package](https://search.nixos.org/packages?channel=unstable&show=emacs29-pgtk&from=0&size=50&sort=relevance&type=packages&query=emacs+pgtk).