[CoreBundle] Don't validate maximum or minimum order quantity when value is 0

[dlhck]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no

Sometimes users enter 0 in the maximum or minimum order quantity and especially when you enter it in the maximum order quantity field, the product can not be added to the cart.

[dpfaffenbauer]

The customer cannot add 0, since the field is validated?!

[dpfaffenbauer]

Anyway, I changed it a bit to allow 0 and 0 disables the behaviour