Improve join_search_one_level readibilty (one line change)

Hello hackers

Attached is my first patch for PostgreSQL, which is a simple one-liner
that I believe can improve the code.

In the "join_search_one_level" function, I noticed that the variable
"other_rels_list" always refers to "joinrels[1]" even when the (level
== 2) condition is met. I propose changing:

"other_rels_list = joinrels[level - 1]" to "other_rels_list = joinrels[1]"

This modification aims to enhance clarity and avoid unnecessary instructions.

I would greatly appreciate any review and feedback on this patch as I
am a newcomer to PostgreSQL contributions. Your input will help me
improve and contribute effectively to the project.

I have followed the excellent guide "How to submit a patch by email,
2023 edition" by Peter Eisentraut.

Additionally, if anyone has any tips on ensuring that Gmail recognizes
my attached patches as the "text/x-patch" MIME type when sending them
from the Chrome client, I would be grateful for the advice.

Or maybe the best practice is to use Git send-email ?

Thank you for your time.

Best regards
Alex Hsieh