Reads from crypto/rand not checked for errors

[mikegorman-nf]

There are a couple of places where reads from crypto/rand are not checked for errors:

secretstream/stream.go

Line 69 in 43e9432

_, _ = rand.Read(k)

secretstream/stream.go

Line 79 in 43e9432

_, _ = rand.Read(header)

While https://pkg.go.dev/crypto/rand#Read does not require a check on the number of bytes read, it should probably have a check for errors. If an error occurs, there may be no read and the key material may be predictable.