Handle mixed activity of literal 0 constant

[wsmoses]

Resolved https://discourse.julialang.org/t/enzyme-jl-cannot-differentiate-through-vector-of-distributions/114338

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 21.95122% with 64 lines in your changes are missing coverage. Please review.

Project coverage is 72.13%. Comparing base (cc8ceb6) to head (8ac770a).
Report is 6 commits behind head on main.

Files	Patch %	Lines
src/compiler.jl	21.95%	64 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1449      +/-   ##
==========================================
+ Coverage   68.04%   72.13%   +4.08%     
==========================================
  Files          30       30              
  Lines       10772    10890     +118     
==========================================
+ Hits         7330     7855     +525     
+ Misses       3442     3035     -407     

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