Fix candidate page 404 errors due to missing district

[lbeaufort]

Summary (required)

Found while testing #2463

• Resolves Candidate with missing district 404's #2499: Fix candidate page 404 errors due to missing district
• Fix candidate page 404 errors due to missing district.
• Only show compare button if link can be generated
• Hide grey box if compare link can't be generated
• (code cleanup) Remove variable self-assignment

Impacted areas of the application

List general components of the application that this PR will affect:

• Candidate profile pages

Screenshots

Before

After

How to test

• Point to dev API
• These pages should load:
  http://localhost:8000/data/candidate/H0CA00116/?tab=summary
  http://localhost:8000/data/candidate/H0CA00116/?tab=about-candidate

[codecov-io]

Codecov Report

Merging #2500 into develop will decrease coverage by 0.1%.
The diff coverage is 44.44%.

@@             Coverage Diff             @@
##           develop    #2500      +/-   ##
===========================================
- Coverage    75.03%   74.92%   -0.11%     
===========================================
  Files          113      113              
  Lines         6929     6932       +3     
  Branches       598      598              
===========================================
- Hits          5199     5194       -5     
- Misses        1730     1738       +8

Impacted Files	Coverage Δ
fec/data/views.py	48.38% <ø> (-0.71%)	⬇️
fec/data/templatetags/filters.py	63.04% <44.44%> (-2.08%)	⬇️
fec/fec/static/js/modules/toc.js	87.17% <0%> (-10.26%)	⬇️

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[johnnyporkchops]

Tested locally, works well. Code looks good.

[JonellaCulmer]

@lbeaufort Just a couple questions, how many candidates would you say this affects? I'm assuming very few. And are they more likely to be new, first-time, filers?

I pulled it down locally and the changes look good/make sense since there's no district and we're unable to compare the candidate to other candidates. At this point, the only thing I would add, and this can go in a followup ticket would be to address the blank committees section.

[lbeaufort]

@JonellaCulmer I'd say pretty few candidates have blank districts, they're usually new filers, and they're usually corrected fairly quickly. I agree about the blank committees section - do you mind putting in an issue?

[JonellaCulmer]

@lbeaufort Great! Yup, I'll put in an issue. But this one looks good otherwise. Will review and merge.

[JonellaCulmer]

This looks great! Thanks for catching!