allow stack_change to be negative #413

Job	Run time
ci / Build	3m 18s
ci / Lint	54s
ci / Test (0)	1m 3s
ci / Typecheck	1m 15s
ci / Test (1)	2m 14s
ci / Test (2)	3m 11s
ci / Test (3)	2m 9s
ci / Test (4)	1m 18s
ci / Test (5)	1m 20s
ci / Test (6)	4m 32s
ci / Test (7)	1m 31s
ci / Test (8)	3m 14s
ci / Test (9)	1m 36s
ci / Publish Unit Tests Results	1s
	27m 36s

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