crypto: fix handling of null BUF_MEM* in ToV8Value() #3624

Job	Run time
Build slim tarball	2m 39s
x86_64-darwin: with shared libraries	33m 11s
aarch64-darwin: with shared libraries	23m 4s
x86_64-linux: with shared libraries	23m 41s
aarch64-linux: with shared libraries	20m 24s
	1h 42m 59s

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