Always defer *sql.Rows.Close and consult with Err (#844)

* Always defer *sql.Rows.Close and consult with Err

database/sql.Rows.Next() makes sure to call Close only after exhausting
result rows which would NOT happen when returning early from a bad Scan.
Close being idempotent makes it a great candidate to get always deferred
regardless of what happens later on the result set.

This change also makes sure call Err() after exhausting Next() and
propagate non-nil results from it as the documentation advises.

Closes #764

Signed-off-by: Kiril Vladimiroff <kiril@vladimiroff.org>

* Override named result parameters in last returns

Signed-off-by: Kiril Vladimiroff <kiril@vladimiroff.org>

* Do the same over new changes that got merged

Signed-off-by: Kiril Vladimiroff <kiril@vladimiroff.org>

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

syncapi/storage/postgres/output_room_events_table.go

@@ -170,6 +170,7 @@ func (s *outputRoomEventsStatements) selectStateInRange(
 	if err != nil {
 		return nil, nil, err
 	}
+	defer rows.Close() // nolint: errcheck
 	// Fetch all the state change events for all rooms between the two positions then loop each event and:
 	//  - Keep a cache of the event by ID (99% of state change events are for the event itself)
 	//  - For each room ID, build up an array of event IDs which represents cumulative adds/removes
@@ -226,7 +227,7 @@ func (s *outputRoomEventsStatements) selectStateInRange(
 		}
 	}
 
-	return stateNeeded, eventIDToEvent, nil
+	return stateNeeded, eventIDToEvent, rows.Err()
 }
 
 // MaxID returns the ID of the last inserted event in this table. 'txn' is optional. If it is not supplied,
@@ -392,5 +393,5 @@ func rowsToStreamEvents(rows *sql.Rows) ([]types.StreamEvent, error) {
 			ExcludeFromSync: excludeFromSync,
 		})
 	}
-	return result, nil
+	return result, rows.Err()
 }