(size_trunc_len): fix Undefined Binary Operator Result. #143

Job	Run time
call-build-freebsd / build-freebsd	3m 3s
call-build-macos / build-macos	1m 36s
call-build-fedora / build-fedora	1m 50s
call-build-alpine / build-alpine	2m 3s
call-build-solaris / build-solaris	5m 3s
call-build-ubuntu / build-ubuntu	5m 12s
	18m 47s

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