Fix invalid handling of pids.limit=0 from runtime spec #5231

Job	Run time
cross-i386	1m 24s
cross-i386 (runc_nodmz)	1m 29s
test (ubuntu-20.04, 1.20.x, rootless, -race)	7m 20s
test (ubuntu-20.04, 1.20.x, rootless)	7m 3s
test (ubuntu-20.04, 1.20.x, -race)	7m 17s
test (ubuntu-20.04, 1.20.x)	6m 40s
test (ubuntu-20.04, 1.21.x, rootless, -race)	7m 38s
test (ubuntu-20.04, 1.21.x, rootless)	7m 13s
test (ubuntu-20.04, 1.21.x, -race)	6m 6s
test (ubuntu-20.04, 1.21.x)	7m 30s
test (ubuntu-20.04, 1.21.x, criu-dev)	6m 54s
test (ubuntu-22.04, 1.20.x, rootless, -race)	10m 50s
test (ubuntu-22.04, 1.20.x, rootless, -race, runc_nodmz)	13m 59s
test (ubuntu-22.04, 1.20.x, rootless)	13m 37s
test (ubuntu-22.04, 1.20.x, rootless, runc_nodmz)	10m 59s
test (ubuntu-22.04, 1.20.x, -race)	10m 3s
test (ubuntu-22.04, 1.20.x, -race, runc_nodmz)	8m 17s
test (ubuntu-22.04, 1.20.x)	7m 57s
test (ubuntu-22.04, 1.20.x, runc_nodmz)	7m 28s
test (ubuntu-22.04, 1.21.x, rootless, -race)	10m 42s
test (ubuntu-22.04, 1.21.x, rootless, -race, runc_nodmz)	12m 24s
test (ubuntu-22.04, 1.21.x, rootless)	10m 22s
test (ubuntu-22.04, 1.21.x, rootless, runc_nodmz)	10m 33s
test (ubuntu-22.04, 1.21.x, -race)	8m 21s
test (ubuntu-22.04, 1.21.x, -race, runc_nodmz)	8m 39s
test (ubuntu-22.04, 1.21.x)	8m 41s
test (ubuntu-22.04, 1.21.x, runc_nodmz)	7m 37s
test (ubuntu-22.04, 1.21.x, criu-dev)	7m 52s
	3h 54m 55s

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