Make aes_hw_ctr32_encrypt_blocks handle len=0 correctly #3101

Job	Run time
haproxy	3m 11s
tpm2-tss	3m 36s
grpc	24m 33s
tcpdump	1m 49s
ntp	2m 17s
Python main	3m 36s
socat	6m 50s
trousers	1m 12s
OpenLDAP	17m 14s
Python releases (FIPS=0 OPENSSL_IN_CRT=0)	12m 30s
bind9	5m 25s
strongswan	1m 49s
Python releases (FIPS=1 OPENSSL_IN_CRT=0)	12m 49s
amazon-corretto-crypto-provider	17m 51s
Python releases (FIPS=0 OPENSSL_IN_CRT=1)	12m 6s
libevent	28m 4s
Python releases (FIPS=1 OPENSSL_IN_CRT=1)	11m 49s
	2h 46m 41s

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