[Rd] dweibull retuns NaN instead of Inf (PR#9080)

[goran.brostrom at gmail.com]

Full_Name: Göran Broström
Version: 2.3.1
OS: Linux, ubuntu
Submission from: (NULL) (85.11.40.53)


> dweibull(0, 0.5, 1)
[1] NaN
Warning message:
NaNs produced in: dweibull(x, shape, scale, log)

should give Inf (and no Warning). Compare with

> dgamma(0, 0.5, 1)
[1] Inf

This happens when 'shape' < 1.