This PR fixes an issue when scanning the snapshots (and history) metadata tables. When the current snapshot for a table is not set, then no snapshots will be returned during the scan. A table can get in this state if it has snapshots, then a REPLACE TABLE operation is performed. In this case, the snapshots are still present but will not be returned because the current snapshot is not set. If some data is committed to the table, and the current snapshot is set to something, then the previous snapshots that were not returned will show up again.

Here is an example on how to reproduce with Spark SQL:

create table local.default.foobar (id int) using iceberg;  
insert into local.default.foobar values (1);  
replace table local.default.foobar (id int, data string) using iceberg;  
select * from local.default.foobar.snapshots; -- no snapshots returned