Consider the prices of built instances of subprojects

[d-buchmann]

This way the total price of a project sums up correctly when it contains subprojects with "built" parts (even if those parts have no explicit shopping information, but a BOM cost). Fixes #1457

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.51%. Comparing base (a0435a5) to head (b1473ca).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1459      +/-   ##
============================================
- Coverage     58.53%   58.51%   -0.02%     
- Complexity     8715     8717       +2     
============================================
  Files           640      640              
  Lines         28199    28201       +2     
============================================
- Hits          16506    16502       -4     
- Misses        11693    11699       +6     

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[jbtronics]

Looks good. Thanks.