Fix encoding crash when LANG environment is empty #1756

Job	Run time
ruby-versions / Generate Ruby versions	3s
ruby-versions / Generate Ruby versions	3s
ruby-versions / Generate Ruby versions	3s
test (2.7)	2m 5s
test (2.7)	1m 44s
test (2.7)	1m 44s
test (3.0)	1m 37s
test (3.0)	1m 37s
test (3.0)	1m 37s
test (3.1)	1m 45s
test (3.1)	1m 45s
test (3.1)	1m 45s
test (3.2)	1m 44s
test (3.2)	1m 44s
test (3.2)	1m 44s
test (3.3)	1m 40s
test (3.3)	1m 40s
test (3.3)	1m 40s
test (3.4)	1m 47s
test (3.4)	1m 47s
test (3.4)	1m 47s
test (debug)	5m 8s
test (debug)	4m 25s
test (debug)	5m 4s
test (head)	1m 34s
test (head)	1m 32s
test (head)	1m 44s
	50m 48s

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