lib: fix modulo sign in webidl convertToInt #5972

Job	Run time
Build slim tarball	3m 8s
collect-openssl-versions	7s
aarch64-linux: Cache V8 build	4s
x86_64-linux: with shared libraries	19m 53s
aarch64-darwin: with shared libraries	19m 55s
x86_64-darwin: with shared libraries	33m 23s
aarch64-linux: with shared openssl_1_1 (1.1.1w)	18m 17s
aarch64-linux: with shared openssl_3 (3.0.19)	19m 35s
aarch64-linux: with shared openssl_4_0 (4.0.0)	19m 23s
aarch64-linux: with shared openssl_3_5 (3.5.5)	18m 37s
aarch64-linux: with shared openssl_3_6 (3.6.1)	19m 39s
	2h 52m 1s

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