char can be signed or unsigned depending on the arch and compiler flags. Use unsigned char explicitly to behave consistently.
Fixes 7078853573 Consolidate Bignum2ByteArray conversion implementations
If we have a QByteArray (ba) and must provide it to
a BIO* expecting OpenSSL function, the following
construct provides it: BioByteArray(ba).ro()
directly providing the QByteArray buffer as BIO
It also supports mixed writes:
BIO_write(bba, buf, size)
bba += QByteArray