function gnansum( N, x, strideX, offsetX ) {
	return gnansumkbn( N, x, strideX, offsetX );
}
Computes the sum of strided array elements, ignoring `NaN` values.

@param {PositiveInteger} N - number of indexed elements
@param {NumericArray} x - input array
@param {integer} strideX - stride length
@param {NonNegativeInteger} offsetX - starting index
@returns {number} sum

@example
var x = [ 2.0, 1.0, 2.0, -2.0, -2.0, 2.0, 3.0, 4.0 ];

var v = gnansum( 4, x, 2, 1 );
// returns 5.0