Use Uint32() instead of Int63() to get pseudo random bytes

As randmath.Int63() returns a non-negative pseudo-random 63-bit integer,
there will be one bit every 64 bits that will always be 0 in the output.

There is no randmath.Uint64() unfortunately, so the next best thing
is to use randmath.Uint32().

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Fix index incremented when it shouldn't be

Index i should only be incremented after b[i] is set.
Otherwise we get some b[i] that always contains 0.

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Merge pull request #5 from chriscool/pseudo_random_fixes

Pseudo random fixes