Coverity spotted that we had an off-by-one here since we were using
`i+1`. Fix this by adding a `-1` to the bounds check. Also use
`sizeof()` to ensure the data and size are coupled.
Coverity CID: 1452207
Closes: #1037
Approved by: jlebon
It's designed for test suites and non-critical random uses like this. This
silences a Coverity warning about weak randomness.
Closes: #1037
Approved by: jlebon
Colin Walters
Giuseppe Scrivano