applyOps accepts invalid UUIDs for the create command

The fuzzer generated the following applyOps entry, which ended up corrupting the system.version collection (newUUID was undefined):

{

        op: 'c',

        ns: 'admin.$cmd',

        ui: newUUID,

        o: { create: 'system.version' }

} 

There could be more validation in applyOps to ensure that the value 'ui' is correct.