clickhouse: fix protocol error for alter table

This fix works because Clickhouse has already closed the stream, so
there's nothing more to be read.  We return an empty driver.Rows so that
it doesn't break the caller's expectations and panic trying to
dereference it's contents.

Author: Alan Braithwaite

clickhouse_read_meta.go

@@ -42,9 +42,8 @@ func (ch *clickhouse) readMeta() (*data.Block, error) {
 			ch.logf("[read meta] <- data: packet=%d, columns=%d, rows=%d", packet, block.NumColumns, block.NumRows)
 			return block, nil
 		case protocol.ServerEndOfStream:
-			_, err := ch.readBlock()
 			ch.logf("[process] <- end of stream")
-			return nil, err
+			return nil, nil
 		default:
 			ch.conn.Close()
 			return nil, fmt.Errorf("[read meta] unexpected packet [%d] from server", packet)

stmt.go

@@ -86,6 +86,15 @@ func (stmt *stmt) queryContext(ctx context.Context, args []driver.NamedValue) (d
 		finish()
 		return nil, err
 	}
+	if meta == nil {
+		sc := make(chan *data.Block)
+		defer close(sc)
+		return &rows{
+			ch:     stmt.ch,
+			finish: finish,
+			stream: sc,
+		}, nil
+	}
 	rows := rows{
 		ch:           stmt.ch,
 		finish:       finish,