worker.sh: read AppStream metainfo under its current name (*.metainfo.xml) too

[budbrain-software]

Problem

code/worker.sh copies in both AppStream file names (lines 385-391):

if [ -e $APPDIR/usr/share/metainfo/*.appdata.xml ] ; then ... fi
if [ -e $APPDIR/usr/share/metainfo/*.metainfo.xml ] ; then ... fi

but it only ever reads *appdata.xml:

if [ -f database/$INPUTBASENAME/*appdata.xml ] ; then      # description
if [ -f database/$INPUTBASENAME/*appdata.xml ] ; then      # screenshot

*.metainfo.xml is the name the AppStream specification asks for today, so any
application using it silently falls back to the .desktop Comment= for the
description and to the automatically taken screenshot — even though its metainfo
file was shipped, copied in, and is perfectly readable.

That it is readable is easy to show: the license block right between those two
ifs already handles both names via *.{appdata,metainfo}.xml, and the license
from such a file does end up in the catalogue entry. Only description and
screenshot are lost.

Change

One variable, used by both blocks, preferring *.appdata.xml when an
application ships both:

AS_XML=$(ls database/$INPUTBASENAME/*.appdata.xml database/$INPUTBASENAME/*.metainfo.xml 2>/dev/null | head -n 1)

As a side effect this also removes two [ -f <glob> ] tests, which fail with
"too many arguments" when an AppDir ships more than one matching file.

Tested

files present	before	after
only *.metainfo.xml	not detected	detected
only *.appdata.xml	detected	detected (unchanged)
both	detected	detected, appdata.xml preferred (unchanged)
neither	falls back	falls back (unchanged)

With a real AppImage shipping only de.budbrain.jsPicPuzzler.metainfo.xml, the
two XPath expressions now return
Jigsaw puzzles from forty photographs, in six sizes and the screenshot URL from
the metainfo, instead of nothing.