The previous code checked whether the progress object had
"outstanding-fetches" set in order to decide whether it had been
initialized enough to show progress information. However, if the
callback saw a progress object on which flatpak_dir_setup_extra_data()
had not yet been called, then it would crash.
Therefore it seems that we should additionally be checking for the
presence of "outstanding-extra-data" which is set in
flatpak_dir_setup_extra_data().
It's likely that this wasn't previously a problem because the callback
would never get called due to the progress object's associated main
context not being iterated. It crashes now because that problem was
fixed in a previous commit.
91f1280e73