Providing 0 as argument for r or p results in a panic:
panic: runtime error: integer divide by zero

Providing negative values for r or p returns a misleading error:
scrypt: parameters are too large

This change avoids the panic and introduces a new error
that is returned when r or p are <= 0:
scrypt: parameters must be > 0

Change-Id: I68987b27d1eedd66644d2ec9436cba364fc1d46d
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/731780
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org>

Update golang.org/x dependencies to their latest tagged versions.

Change-Id: I1b283104f6d4557ee12c256bbadfccb3cd5548be
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/743362
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Gopher Robot <gobot@golang.org>