checker: fix structinit validation on nested generic Map[K]V (fix #23… #403

Job	Run time
tests-sanitize-address-clang	2h 29m 58s
tests-sanitize-address-gcc	2h 15m 54s
tests-sanitize-address-msvc	3m 50s
tests-sanitize-memory-clang	2h 44m 17s
tests-sanitize-undefined-gcc	57m 39s
tests-sanitize-undefined-clang	43m 23s
	9h 15m 1s

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