Bug - NaN Map Dimensions are handled silently and inconsistently

[NickStafford]

Hi,

Feel free to explain if this is intended behaviour but it definitely looks like a bug to me.

What happened

When creating a new Map() if NaN values get in to the dimensions (e.g. new Map(NaN, NaN)) then a Map object is created with no warnings.

If you zoom such a Map object using zoomToBox(), you get a Map object with inconsistent extents.

This causes problems later on when trying to manipulate the Map.

Example

testFunction() {
    console.log('Creating map...');

    if (mapnik.register_default_input_plugins) mapnik.register_default_input_plugins();

    var srs = '+init=epsg:4326';
    var map = new mapnik.Map(NaN, NaN, srs);

    console.log('Map created...');
    console.log(map);

    map.loadSync(resolve('./samples/stylesheet.xml'));
    console.log('Map stylesheet loaded...');

    map.zoomToBox(0, 0, 5000000, 5000000);
    console.log('Map zoomed...');

    console.log(map.extent);

    map.renderFileSync('/tmp/map.png');
    console.log('Map rendered...');

    let data = fs.readFileSync('/tmp/map.png');
    console.log('Map data read...');

    await SaveToS3('map.png', data);
    console.log('Map data saved to S3...');
}

The above function results in the following output:

Note how the x dimension extents are limited to NaN and the y coordinates are not.

What I expected

I expected Maps with NaN dimensions to be invalid and error, or at the very least produce a warning.

I would also expect that even if the Map is created in this situation, since both Map dimensions are NaN it would treat the x and y parts of the zoom consistently and either they would all assign correctly, or they would all NaN (or even better produce an error / warning feedback as to what was going on).

Ideally I'd say situations like this should reject creating the map.