Fix #14945 FN memleak with nested scopes. #20515

Job	Run time
build_make (ubuntu:25.10)	3m 44s
build_make (alpine:3.23)	4m 28s
build_cmake (alpine:3.23, false, false)	4m 35s
build_make (ubuntu:24.04)	3m 6s
build_cmake (ubuntu:24.04, true, true)	2m 57s
build_cmake (ubuntu:25.10, true, true)	3m 6s
	21m 56s

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