When the going from the region panel to the overview and back,
the input methods in the list loose their display names. What
is happening is that we recreate the ibus object, but the second
time around it is already connected since ibus uses a shared
singleton connection internally. Thus, the ::connected signal
is never emitted, and we don't fetch the engines.
Work around this by checking if the newly created ibus object
is already connected, and directly calling fetch_ibus_engines
if it is. To make this work, we have to set up the treeview
with its model earlier.
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