Fix bug in GML parsing

When parsing the gml:Envelope tag, only one point was inserted into the obj struct, causing the max assignment to fail.

This code corrects the problem.

The following snippet can be used to test the code, but I couldn't figure out how to wrap it up so the parser would parse it:

<gml:Envelope srsName="EPSG:1234"><gml:pos>111 222</gml:pos><gml:pos>333 444</gml:pos></gml:Envelope>

Also, I am not sure why there is a comment in the notes/2.13.md file -- this was, I believe, already committed to the main code repository a while back.