public Task<int> UpdateAsync(object poco, IEnumerable<string> columns) does not work with POCO that has string primary key

[groogiam]

The update overload does not resolve the primary key correctly for entities with string primary keys when columns are specified. The issue looks to be around line 1303 of Database.cs where the pk is resolved if no columns are specified but is not when columns are specified. Attached is a repro of the issue.
UpdateTest.zip