🚸 Add OptimizeNotCalled error

[blegat]

It should resolve the issue of #1739 (comment)

[mlubin]

This looks reasonable. Note the doctest failures.

[codecov]

Codecov Report

Merging #1766 into master will increase coverage by 0.05%.
The diff coverage is 81.25%.

@@            Coverage Diff             @@
##           master    #1766      +/-   ##
==========================================
+ Coverage   69.09%   69.14%   +0.05%     
==========================================
  Files          30       30              
  Lines        3944     3957      +13     
==========================================
+ Hits         2725     2736      +11     
- Misses       1219     1221       +2

Impacted Files	Coverage Δ
src/JuMP.jl	71.9% <81.25%> (+0.6%)	⬆️
src/objective.jl	95% <0%> (+5%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 798258d...e5aa164. Read the comment docs.

[codecov]

Codecov Report

Merging #1766 into master will increase coverage by 0.3%.
The diff coverage is 81.25%.

@@            Coverage Diff            @@
##           master    #1766     +/-   ##
=========================================
+ Coverage   69.09%   69.39%   +0.3%     
=========================================
  Files          30       30             
  Lines        3944     4013     +69     
=========================================
+ Hits         2725     2785     +60     
- Misses       1219     1228      +9

Impacted Files	Coverage Δ
src/JuMP.jl	71.9% <81.25%> (+0.6%)	⬆️
src/objective.jl	95% <0%> (+5%)	⬆️
src/constraints.jl	79.19% <0%> (+5%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 798258d...e5aa164. Read the comment docs.