update zip script

zip.sh

@@ -12,7 +12,9 @@ for f in *.mokuro; do
     base="${f%.mokuro}"
     dir="$base"
     zipfile="$base.zip"
-    if [ -d "$dir" ]; then
+    if [[ -f "$zipfile" ]]; then
+        echo "Warning: Zip file $zipfile already exists, skipping."
+    elif [ -d "$dir" ]; then
         echo "Zipping: $zipfile <- $f $dir/"
         zip -qr "$zipfile" "$f" "$dir"
     else