Fix message author name in muc chat

The username of the message author name was not set
and thus the database were being filled with empty
names

This was broken in b116a95f
8 jobs for wip/sadiq/fix-muc-username in 19 minutes and 48 seconds (queued for 18 minutes and 3 seconds)
Status Job ID Name Coverage
  Build
passed #296751
librem5
build-debian-gcc-bullseye

00:03:11

passed #296750
librem5
build-debian-gcc-buster

00:02:58

 
  Test
passed #296753
librem5
check-po

00:00:28

passed #296752
librem5
test:debian-gcc

00:02:47

16.8%
 
  Package
passed #296754
librem5
package:deb-debian-buster

00:03:05

passed #296755
librem5:arm64
package:deb-debian-buster:arm64

00:07:26

 
  Test Package
passed #296756
librem5
autopkgtest-debian-buster-package

00:02:00

passed #296757
librem5
lintian-debian-buster-package

00:00:53