Handle undefined field on unique constraint error (#10016)

[jusguy]

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• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
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Description of change

Change to AbstractQuery.getUniqueConstraintErrorMessage() to handle falsey field. This fixes the TypeError in #10016.

Closes #10016

[codecov]

Codecov Report

Merging #10018 into master will increase coverage by 7.09%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #10018      +/-   ##
==========================================
+ Coverage   89.29%   96.39%   +7.09%     
==========================================
  Files          61       63       +2     
  Lines        9293     9391      +98     
==========================================
+ Hits         8298     9052     +754     
+ Misses        995      339     -656

Impacted Files	Coverage Δ
lib/dialects/sqlite/index.js	100% <ø> (ø)	⬆️
lib/dialects/abstract/index.js	100% <ø> (ø)	⬆️
lib/dialects/postgres/index.js	100% <ø> (ø)	⬆️
lib/dialects/abstract/query.js	91.34% <100%> (ø)	⬆️
lib/dialects/mssql/connection-manager.js	88.6% <0%> (ø)
lib/dialects/mssql/index.js	100% <0%> (ø)
lib/model.js	96.66% <0%> (+0.06%)	⬆️
lib/sequelize.js	96.58% <0%> (+0.62%)	⬆️
lib/query-interface.js	91.11% <0%> (+0.98%)	⬆️
lib/dialects/abstract/query-generator.js	97.65% <0%> (+4.07%)	⬆️
... and 6 more

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[sushantdhiman]

Thanks @justinkalland