[units.wesnoth.org] improve safeguard

...against overwriting the last successful version

data/tools/unit_tree/update-wmlunits

@@ -47,6 +47,7 @@ $TOOLS/wesnoth_addon_manager -p $PORT -d '.*' -c $ADDONS > $LOG/wesnoth_addon_ma
 echo WORKING
 python -u $TOOLS/wmlunits -t $TRANS -D $DATA -o $TMPOUT -w $EXE -C $CONFIG -a $ADDONS -L $DIR/overview.txt -B $DIR/overview.txt -T $TIMEOUT > $LOG/wmlunits.txt 2>&1
 test -f $TMPOUT/mainline/en_US/mainline.html
+test -f $TMPOUT/pics/core$images$units$woses$wose.png
 rsync -vaz --delete $TMPOUT/ $OUT > $LOG/rsync.txt 2>&1
 rm -rf $TEMP/*
 rm -rf $TMPOUT