barrier=wall forming closed way is a line, not an area

[matkoniecz]

For start, thanks for this tool - it is extremely useful! Right now I am using it in making a 3D tactile map for blind children :)

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="Overpass API 0.7.56.9 76e5016d">
<note>The data included in this document is from www.openstreetmap.org. The data is made available under ODbL.</note>
<meta osm_base="2021-05-21T07:19:41Z"/>

  <way id="414631278">
    <nd ref="4157482778"/>
    <nd ref="4157482783"/>
    <nd ref="4157482775"/>
    <nd ref="4157482773"/>
    <nd ref="4157482778"/>
    <tag k="barrier" v="wall"/>
  </way>
  <node id="4157482773" lat="50.0548978" lon="19.9265210"/>
  <node id="4157482775" lat="50.0549340" lon="19.9266089"/>
  <node id="4157482778" lat="50.0549590" lon="19.9264641"/>
  <node id="4157482783" lat="50.0549945" lon="19.9265503"/>

</osm>

is incorrectly converted to "type": "Polygon"

Not making a PR as there are ancient not reviewed PRs (#114 from 2019 is neither accepted nor rejected nor reviewed)