Diff command crashes if second input file has no timestamp

[Nakaner]

build/osmium diff --output-format opl test/diff/input1.osm test/diff/input2-only-version.osm crashes because an assertion fails:

osmium: /home/michael/git/libosmium/include/osmium/io/input_iterator.hpp:129: 
osmium::io::InputIterator<TSource, TItem>::value_type* 
osmium::io::InputIterator<TSource, TItem>::operator->() const 
[with TSource = osmium::io::ReaderWithProgressBar; TItem = osmium::OSMObject; 
osmium::io::InputIterator<TSource, TItem>::pointer = osmium::OSMObject*; 
osmium::io::InputIterator<TSource, TItem>::value_type = osmium::OSMObject]: 
Assertion `m_iter' failed.

The input file test/diff/input2-only-version.osm has following content:

<?xml version='1.0' encoding='UTF-8'?>
<osm version="0.6" generator="test">
  <node id="10" version="1" lat="1" lon="1"/>
  <node id="11" version="2" lat="2" lon="2"/>
  <node id="12" version="1" lat="3" lon="1"/>
  <node id="14" version="1" lat="5" lon="1"/>
  <node id="15" version="1" lat="5" lon="1"/>
  <node id="16" version="1" lat="5" lon="1"/>
  <way id="20" version="1">
    <nd ref="10"/>
    <nd ref="11"/>
    <nd ref="12"/>
    <tag k="foo" v="bar"/>
  </way>
  <way id="21" version="2">
    <nd ref="12"/>
    <nd ref="14"/>
    <tag k="xyz" v="new"/>
  </way>
  <relation id="30" version="1">
    <member type="node" ref="12" role="m1"/>
    <member type="way" ref="20" role="m2"/>
  </relation>
</osm>

Reason: The comparison *it2 < *it1 at line 274 is the problem because iterator it2 has already reached the end (i.e. it2 == end2 would return true).

Using a different comparator ignoring the timestamp as done in my attempt to make the derive-changes command work with missing timestamps does not help.

[joto]

I think I just fixed this. Can you verify?

[Nakaner]

It works. I will submit it as a unit test in a pull request.