fix "window `NULL` issue" (hopefully)

There were multiple reports where after a reconnect the window of the
MUC that was last opened, was empty.

`muc_join()` creates an instance of a MUC, `presence_join_room()` works
with this instance. Therefore the instance has to exist before working on
it.

I'm not sure if this really fixes the issue, but at least it didn't
happen anymore after I applied this modification.
I can't remember how I stumbled over this, either while looking at debug
logs or while looking at Valgrind output while a reconnect happened, but
something went wrong. Then I came to the conclusion that this may fix
the issue and for now it did ... maybe it comes back, then my RCA was
wrong.

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

0 files changed, 0 insertions, 0 deletions