GetAggregatedIntProperty() broken when one column lacks the property.

#### Background
I have disabled the block_cache on the "default" column by setting the `no_block_cache` table option. This prevents the internal default creation of that cache. The rest of my columns have block caches.

##### Actual behavior
Calling `GetAggregatedIntProperty()` returns false with the keys:
- `rocksdb.block-cache-capacity`
- `rocksdb.block-cache-usage`
- `rocksdb.block-cache-pinned-usage`

##### Expected behavior
The aggregation should count a missing property for a column as zero. The other columns should continue to be accumulated without being disrupted by one column missing the property. In this case I want the total cache properties for all of my columns; a column without a cache merely adds zero to these properties. It should not be an error.