Fix for #511

[torfjelde]

Because we add a return to the last statement in the model body before replacing returns + we don't recursively call replace_returns! on the args to the return statement, we run into issues when the last statement in the body itself contains return (as in #511).

This PR addresses this issue.

[codecov]

Codecov Report

Patch coverage: 75.00% and project coverage change: +0.02% 🎉

Comparison is base (5dd7c53) 75.47% compared to head (11acfd4) 75.49%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #512      +/-   ##
==========================================
+ Coverage   75.47%   75.49%   +0.02%     
==========================================
  Files          23       23              
  Lines        2764     2763       -1     
==========================================
  Hits         2086     2086              
+ Misses        678      677       -1     

Files Changed	Coverage Δ
src/compiler.jl	93.65% <75.00%> (+0.45%)	⬆️

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[torfjelde]

Feel free to merge this as soon as someone has approved and the tests have passed 👍

[github-actions]

Pull Request Test Coverage Report for Build 5764647699

• 3 of 4 (75.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 75.498%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/compiler.jl	3	4	75.0%

Totals
Change from base Build 5707142959:	0.03%
Covered Lines:	2086
Relevant Lines:	2763

---

💛 - Coveralls

[devmotion]

Not completely familiar with the previous implementation but looks good to me.