crypto: guard against size_t overflow on experimental 32-bit arch #5139

Job	Run time
Build slim tarball	2m 51s
aarch64-linux: with shared libraries	18m 13s
x86_64-darwin: with shared libraries	27m 36s
aarch64-darwin: with shared libraries	16m 45s
x86_64-linux: with shared libraries	21m 21s
	1h 26m 46s

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