Indexing / geometry / avoid multicurve GML feature

[fxp]

When extracting bounding "polygon", we may end up trying to convert MultiCurve to Polygon which trigger errors and record is not indexed. Do not support MultiCurve in indexing (we can't mix geometries in shapefile BTW)

      <!-- MIKADO AUTOMATIC var63=[-76.816333 ... -57.079131] (Curves-coordinates) MULTIPLE / OPTIONAL -->
      <gml:posList>-76.816333 -36.777203 -77.192141 -43.722611 -80.198605 -47.195299 -78.319565 -50.400867 -74.561741 -54.674947 -70.052045 -57.079131</gml:posList>
    </gml:LineString>
  </gml:curveMember>
</gml:MultiCurve>
	class com.vividsolutions.jts.geom.MultiLineString cannot be converted to a polygon. Check Metadata
java.lang.IllegalArgumentException: class com.vividsolutions.jts.geom.MultiLineString cannot be converted to a polygon. Check Metadata
	at org.fao.geonet.kernel.search.spatial.SpatialIndexWriter.toMultiPolygon(SpatialIndexWriter.java:453)

[fxp]

master commit 3bbfe6460f9e3c5bf6d84f50f18aa74e12395756