database: Fix using sqlite-reset in a few queries.

Rather than calling sqlite-reset before reading the rows, call sqlite-reset
after. I think this is important to stop SQLite getting stuck because the
statement is still live even though it's not being read from after these
procedures return.

Assuming I've got the ordering right, I think using sqlite-fold-right directly
is simpler code as well.

* src/cuirass/database.scm (db-get-builds-by-search, format-build-products,
db-get-events): Rewrite fetching result rows.