poly plugin: should warn about unclosed ways or properly merge them, if possible

[naoliv]

Open the attached example.osm file and save it as a Osmosis poly file.

See how empty the new poly file is:

example
END

Couldn't we have a warning about such cases, when we have unclosed ways in the data to be exported?
Or better, if possible, merge the ways to properly form a closed area.

JOSM:

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2017-04-17 23:55:53 +0200 (Mon, 17 Apr 2017)
Build-Date:2017-04-18 01:33:31
Revision:11950
Relative:URL: ^/trunk

Identification: JOSM/1.5 (11950 pt_BR) Linux Debian GNU/Linux 9.0 (stretch)
Memory Usage: 475 MB / 10206 MB (109 MB allocated, but free)
Java version: 1.8.0_121-8u121-b13-4-b13, Oracle Corporation, OpenJDK 64-Bit Server VM
Screen: :0.0 1600x900, :0.1 1280x1024
Maximum Screen Size: 1600x1024
Java package: openjdk-8-jre:amd64-8u121-b13-4
Java ATK Wrapper package: libatk-wrapper-java:all-0.33.3-13
VM arguments: [-Dawt.useSystemAAFontSettings=on]
Dataset consistency test: No problems found

Plugins:
+ Create_grid_of_ways (32699)
+ FastDraw (33182)
+ ImportImagePlugin (33028)
+ OpeningHoursEditor (33185)
+ PicLayer (33148)
+ RoadSigns (33204)
+ SimplifyArea (33004)
+ apache-commons (32994)
+ buildings_tools (33004)
+ conflation (0.5.4)
+ contourmerge (1030)
+ download_along (32946)
+ editgpx (33004)
+ ejml (32680)
+ geojson (52)
+ geotools (33042)
+ importvec (33088)
+ indoorhelper (33088)
+ jts (32699)
+ log4j (32699)
+ measurement (33088)
+ merge-overlap (33154)
+ opendata (33245)
+ pbf (33241)
+ pdfimport (33004)
+ poly (33004)
+ reverter (33088)
+ scripting (30764)
+ tageditor (33021)
+ todo (30100)
+ turnlanes (33088)
+ turnlanes-tagging (254)
+ turnrestrictions (33088)
+ undelete (33263)
+ utilsplugin2 (33212)