Fixes #787 - Added guards in CartEndpoint to protected against NullOrderImpl along with null from CartState
Merge branch 'BroadleafCommerce-3.0.x' into BroadleafCommerce-3.1.x

Conflicts:
	core/broadleaf-framework-web/src/main/java/org/broadleafcommerce/core/web/api/endpoint/order/CartEndpoint.java
Merge remote-tracking branch 'origin/BroadleafCommerce-3.1.x' into BroadleafCommerce-3.1.x