[BcMathNumber::performOperation] Specified scale 0 conflict

[fyrye]

The determination of scale in BcMathNumber::performOperation returns unexpected results.

$scale = (int) ($scale ?: self::$defaultScale);

Will return as self::defaultScale when a scale of 0 is specified.
e.g.

echo BcMathNumber::create('123.45')
   ->add('1', 0)
   ->getValue(); 
   //returns 124.45000000 - expected 124

vs https://3v4l.org/ib3ZC

echo bcadd('123.45', '1', 0); //124

The line should be changed to read:

$scale = (int) (null === $scale ? self::$defaultScale : $scale);

[dbojdo]

@fyrye Thanks for pointing it out. I've put some tests in place to cover this case and I've fixed some more issues I've found during this.