fix Weibull PDF at X=Inf

[brgirgis]

No description provided.

[codecov]

Codecov Report

Merging #28 (2b656ea) into master (07bc727) will decrease coverage by 0.63%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   92.87%   92.24%   -0.64%     
==========================================
  Files         184      156      -28     
  Lines        3706     3390     -316     
==========================================
- Hits         3442     3127     -315     
+ Misses        264      263       -1     

Impacted Files	Coverage Δ
include/stats_incl/dens/dweibull.ipp	100.00% <100.00%> (ø)
include/stats_incl/rand/rnorm.ipp	88.88% <0.00%> (-6.12%)	⬇️
include/stats_incl/rand/rbern.ipp	100.00% <0.00%> (ø)
include/stats_incl/rand/rchisq.ipp	100.00% <0.00%> (ø)
tests/rand/rbeta.cpp
tests/rand/rbern.cpp
tests/rand/rweibull.cpp
tests/rand/rinvwish.cpp
include/stats_incl/rand/rcauchy.ipp
... and 25 more

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[kthohr]

Thanks for the PR.