Address Undefined Arguments Error in comparePassword

[raclim]

Addresses Server Log (pictured below) that identifies undefined arguments being passed to the comparePassword() method in the user model.

Changes:

• Checks if this.password exists before calling bcrypt.compare
• Adds explicit try/catch and error messaging

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

[release-com]

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