Fixes #983 - Prevent NPE when adding/update Pages and Structured Content when validating

(cherry picked from commit 258cca244a5f101e7c6920de758d06476dc9d7f5)

Conflicts:
	admin/broadleaf-open-admin-platform/src/main/java/org/broadleafcommerce/openadmin/server/service/persistence/validation/EntityValidatorService.java
	admin/broadleaf-open-admin-platform/src/main/java/org/broadleafcommerce/openadmin/server/service/persistence/validation/EntityValidatorServiceImpl.java