Fix incorrect result if null partition fields in orc file.
### Root Cause
Theoretically, the underlying file of the hive partition table should not contain partition fields. But we found that in some user scenarios, the partition field will exist in the underlying orc/parquet file and are null values. As a result, the pushed down partition field which are null values. filter incorrectly.
### Solution
we handle this case by only reading non-partition fields. The parquet reader is already handled this way, this PR handles the orc reader.
8af1e7f27f