Fix fetching tmpTables vs tmpDiskTables from performance_schema

The `perf_schema.eventsstatements` collector was incorrectly exposing
"tmp_tables" as "tmp_disk_tables" and vice versa, due to query result
being scanned in incorrect order.

Closes #849

collector/perf_schema_events_statements.go

@@ -192,7 +192,7 @@ func (ScrapePerfEventsStatements) Scrape(ctx context.Context, db *sql.DB, ch cha
 	)
 	for perfSchemaEventsStatementsRows.Next() {
 		if err := perfSchemaEventsStatementsRows.Scan(
-			&schemaName, &digest, &digestText, &count, &queryTime, &errors, &warnings, &rowsAffected, &rowsSent, &rowsExamined, &tmpTables, &tmpDiskTables, &sortMergePasses, &sortRows, &noIndexUsed,
+			&schemaName, &digest, &digestText, &count, &queryTime, &errors, &warnings, &rowsAffected, &rowsSent, &rowsExamined, &tmpDiskTables, &tmpTables, &sortMergePasses, &sortRows, &noIndexUsed,
 		); err != nil {
 			return err
 		}