csgrep --warning-rate-limit: fix key events out of range #344

Job	Run time
Ubuntu 20.04 (clang++)	2m 11s
Ubuntu 22.04 (clang++ with sanitizers)	3m 46s
Ubuntu 20.04 (g++)	1m 56s
Ubuntu 22.04 (g++ with sanitizers)	5m 25s
	13m 18s

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