ValidateBatch fails on delete op

For delete op, there is no meta or value, but ValidateBatch would still validate batch has meta and value.

@@ -626,12 +635,14 @@ Status MagmaKVStore::validateBatch(CRecord* recs, size_t nrecs) {
if (!IsValidKey(&recs[i].Key))

{ return Status(Status::Code::Invalid, "Invalid Batch Key"); }

if (!IsValidVal(&recs[i].Val))

{ return Status(Status::Code::Invalid, "Invalid Batch Val"); }

if (!IsValidMeta(&recs[i].Meta))

{ return Status(Status::Code::Invalid, "Invalid Batch Meta"); }

}