fix js falsy values convert

[maRci002]

Hello, in some cases long0 gets wrong value if longc is 0 and messes up the result of proj4js. Here is an example:

// EPSG:6932
var proj4Def = '+proj=laea +lat_0=-90 +lon_0=0 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs';
// in ogc wkt 'longitude_of_center' is 0
var ogcWktDef = 'PROJCS["WGS 84 / NSIDC EASE-Grid 2.0 South",GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_center",-90],PARAMETER["longitude_of_center",0],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["X",EAST],AXIS["Y",NORTH],AUTHORITY["EPSG","6932"]]';
var esriWktDef = 'PROJCS["Lambert_Azimuthal_Equal_Area",GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137,298.257223563]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295]],PROJECTION["Lambert_Azimuthal_Equal_Area"],PARAMETER["latitude_of_origin",-90],PARAMETER["central_meridian",0],PARAMETER["false_easting",0],PARAMETER["false_northing",0],UNIT["Meter",1]]';

var point = [17.888058560281515, 46.89226406700879];

console.log(proj4('WGS84', proj4Def, point)); // [3638523.4746012595, 11273118.062993607]
console.log(proj4('WGS84', ogcWktDef, point)); // [NaN, NaN]
console.log(proj4('WGS84', esriWktDef, point)); // [3638523.4746012595, 11273118.062993607]

[NaN, NaN] should be: [3638523.4746012595, 11273118.062993607]

In proj4dart we did some bulk tests with 8500 projdefs (from PostGIS) and this caused a little mess :smiley: