Shell UISelect options are set with partial values when auto-completing

FORGE-1537 introduced a validation for invalid values in UISelectOne/Many components. However, during auto-completion, the shell implementation attempts to set the partial value (correctly converted to null, because it is not present in the value choices)
Eg:

jpa-setup --container JB<TAB>

The validation in https://github.com/forge/core/blob/master/ui/api/src/main/java/org/jboss/forge/addon/ui/util/InputComponents.java#L213 is the culprit. Removing it, the value is correctly set to null, however it breaks FORGE-1537.