Change beziePathWithRect into beziePath not to evaluate CGRectNull

Hi, there.

I'm using the library.
So, nice!!
But, I'm feeling a bad performance when not showing outer-shadow from centerViewController.

The cause of the incident has happened with using CGRectNull to beziePathWithRect.

So, I've removed it.

Thank you for your consideration in advance!

Best regarda,

kaneshin