Fixes error when using EagerLoad on a relationship

[bart-degreed]

Fixes #988.

I intentionally haven't added tests, because [EagerLoad] was never meant to be combined with relationship attributes. This PR does not make that a supported feature. Instead this fix is solely to unblock a user that ran into a problem while trying to do so. In that process, additional problems may surface and we'll see how to deal with them on a case-by-case basis.

A few tests exist in unmerged #990, which was used to reproduce the problem.

[codecov]

Codecov Report

Merging #1000 (024f1c7) into master (e34709d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 024f1c7 differs from pull request most recent head 70abcd5. Consider uploading reports for the commit 70abcd5 to get more accurate results

@@           Coverage Diff           @@
##           master    #1000   +/-   ##
=======================================
  Coverage   91.38%   91.39%           
=======================================
  Files         283      283           
  Lines        7537     7539    +2     
=======================================
+ Hits         6888     6890    +2     
  Misses        649      649           

Impacted Files	Coverage Δ
.../Internal/QueryableBuilding/SelectClauseBuilder.cs	94.28% <100.00%> (+0.11%)	⬆️

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