Fix two issues with custom_query_jumble in gen_node_support.pl

Fix two issues with custom_query_jumble in gen_node_support.pl

A node field marked with custom_query_jumble and query_jumble_ignore
would generate some code of a custom routine.  The script is changed so
as custom_query_jumble behaves like the other options in this case,
query_jumble_ignore taking priority, with no code generated.

A comment related to the code generated for node types was misplaced.

Thinkos introduced in 5ac462e2b7ac.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/1324036.1742945060@sss.pgh.pa.us