Rollup merge of #58654 - estebank:underflow, r=nikomatsakis
Rollup merge of #58654 - estebank:underflow, r=nikomatsakis

Do not underflow after resetting unmatched braces count

Fix #58638.

r? @oli-obk

graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust