Check for sitemaps.log instead of sitemaps directory

Fixes a bug where absence of sitemap directory is preventing sitemaps from being run after `--overwrite` deletes `sitemaps/` directory.

Closes #7581, correctly implements #11625

Author: mekarpeles

scripts/oldump.sh

@@ -220,7 +220,7 @@ fi
 # =================
 # Generate Sitemaps
 # =================
-if [[ ! -d $TMPDIR/sitemaps ]]
+if [[ ! -f $TMPDIR/sitemaps/sitemaps.log ]]
 then
     log "generating sitemaps"
     mkdir -p $TMPDIR/sitemaps