[PATCH] wallpapers/image: don't crash when removing /usr/share

[PATCH] wallpapers/image: don't crash when removing /usr/share

we delay addSourceModel when the source model is fully loaded,
but it might take a long time (ie adding /usr/share)

if then we remove it before it's done, we will have either an assert or a crash
in qconcatenatetablesmodel (depending if Qt asserts are turned on)

we can safely call addsourceModel immediately, so rowsInserted will be
forwarded as they come in

BUG:503593

(cherry picked from commit f584f1beb3aaafe36c328a761b8eea02b46f20c4)

f584f1be wallpapers/image: don't crash when removing /usr/share

Co-authored-by: Marco Martin <notmart@gmail.com>
Gbp-Pq: Name upstream_e9fd71d9_wallpapers-image-don-t-crash-when-removing-usr-share.patch