Handle and test zero-size inputs to RNGs.

[maleadt]

Fixes #2093

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (43370c5) 71.73% compared to head (ac017e9) 71.72%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2098      +/-   ##
==========================================
- Coverage   71.73%   71.72%   -0.01%     
==========================================
  Files         157      157              
  Lines       13853    13867      +14     
==========================================
+ Hits         9937     9946       +9     
- Misses       3916     3921       +5     

Files	Coverage Δ
src/random.jl	63.84% <100.00%> (+0.41%)	⬆️
lib/curand/random.jl	72.65% <69.23%> (-0.62%)	⬇️

... and 1 file with indirect coverage changes

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