Fix int_plus_one warnings #3670

Job	Run time
Check Access Permissions	1s
Check Packages and Shards	1m 27s
Mutation Testing - Shards, Stackslib (0)	1h 47m 31s
Mutation Testing - Shards, Stackslib (1)	1h 48m 9s
Mutation Testing - Normal, Stackslib	0s
Mutation Testing - Shards, Stackslib (2)	58m 6s
Mutation Testing - Shards, Small	0s
Mutation Testing - Normal, Small	0s
Mutation Testing - Shards, Stackslib (3)	1h 1m 39s
Mutation Testing - Shards, Stackslib (4)	1m 47s
Mutation Testing - Normal, Stacks Node	0s
Mutation Testing - Shards, Stackslib (5)	1m 41s
Mutation Testing - Shards, Stacks Node	0s
Mutation Testing - Normal, Stacks Signer	0s
Mutation Testing - Shards, Stackslib (6)	1m 43s
Mutation Testing - Shards, Stackslib (7)	2m 49s
Output Mutants	3s
	5h 44m 56s

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