Fixed wrong conditions for getting Gift Wrapper prices (new PR for develop branch)

from @rogyar 

Magento EE on the following request:

$address->getGwPrice()
might return (string) "0.0000"

Then condition

 if($address->getGwPrice())
will be TRUE 
It causes unnecessary calculations and even wrong taxes calculation. 
Glad to share this little fix with you. 
Thanks.