[pixels-planner] incorrect join plan for single-pipeline broadcast join after complete broadcast chain join.

[bianhq]

For tpch-1g, when the column statistics are collected and the row counts for each table are 0, trino generates a join plan for q8 like this:

In pixels planner, the blue and green parts are converted to broadcast-chain-join 1 and 2, respectively.
The root of the join plan (red) is a large-left broadcast join, in which the left table is the join result of broadcast-chain-join 2.

However, pixels planner continues to add the root into broadcast-chain-join 2, replacing the right node broadcast-chain-join 1 with the base table part, and forming an incorrect physical join plan like this:

The three tables in broadcast-chain-join 1 of the original join plan are missing.

[bianhq]

Fixed.