Fix rewrite generic of sum(::Symbol; init)

[odow]

x-ref https://discourse.julialang.org/t/jump-reports-an-error-when-attempting-to-sum-the-empty-denseaxisarray-as-the-objective-function/133332/3

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.86%. Comparing base (ffcfd9a) to head (09ce663).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #339      +/-   ##
==========================================
- Coverage   90.56%   89.86%   -0.71%     
==========================================
  Files          22       22              
  Lines        2269     2141     -128     
==========================================
- Hits         2055     1924     -131     
- Misses        214      217       +3     

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