Handle empty JSON in LogEntry on new save

[rnovak338]

Addresses #4517.

Sometimes with Django Admin, there are no actual changes made by the staffuser when attempting to save edits to a record in the DB. Currently on production, this will break things and create a 500 response. This PR creates a condition that verifies that JSON exists before parsing.

How to test

1. Get into Django Admin on your local startup. (Start app once, log in to your email from staffusers.json, restart app, visit /admin).
2. Create a record in TribalApiAccessKeyIds. Save changes.
3. Reopen this record from the table in Django Admin. Do not make any changes, and save again.
4. Rather than 500, you should get a successful response.
5. Check the LogEntry table at the top of the models list to see your change.

The LogEntry should resemble this screenshot.

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[github-actions]

Terraform plan for meta

No changes. Your infrastructure matches the configuration.

No changes. Your infrastructure matches the configuration.

Terraform has compared your real infrastructure against your configuration
and found no differences, so no changes are needed.

✅ Plan applied in Deploy to Development and Management Environment #879

[github-actions]

Terraform plan for dev

Plan: 1 to add, 0 to change, 1 to destroy.

Terraform used the selected providers to generate the following execution
plan. Resource actions are indicated with the following symbols:
-/+ destroy and then create replacement

Terraform will perform the following actions:

  # module.dev.module.cors.null_resource.cors_header must be replaced
-/+ resource "null_resource" "cors_header" {
!~      id       = "*******************" -> (known after apply)
!~      triggers = { # forces replacement
!~          "always_run" = "2024-12-09T16:26:12Z" -> (known after apply)
        }
    }

Plan: 1 to add, 0 to change, 1 to destroy.

✅ Plan applied in Deploy to Development and Management Environment #879

[github-actions]

Package	Line Rate	Branch Rate	Health
.	100%	100%	✔
api	98%	90%	✔
audit	97%	87%	✔
audit.cross_validation	98%	88%	✔
audit.fixtures	84%	50%	❌
audit.intakelib	90%	81%	➖
audit.intakelib.checks	92%	85%	➖
audit.intakelib.common	98%	82%	✔
audit.intakelib.transforms	100%	95%	✔
audit.management.commands	78%	17%	❌
audit.migrations	100%	100%	✔
audit.models	93%	75%	➖
audit.templatetags	100%	100%	✔
audit.views	62%	41%	❌
census_historical_migration	96%	65%	✔
census_historical_migration.migrations	100%	100%	✔
census_historical_migration.sac_general_lib	92%	84%	➖
census_historical_migration.transforms	95%	90%	✔
census_historical_migration.workbooklib	68%	69%	❌
config	77%	27%	❌
curation	100%	100%	✔
curation.curationlib	57%	100%	❌
curation.migrations	100%	100%	✔
dissemination	91%	72%	➖
dissemination.migrations	97%	25%	✔
dissemination.searchlib	74%	64%	❌
dissemination.templatetags	100%	100%	✔
djangooidc	53%	38%	❌
djangooidc.tests	100%	94%	✔
report_submission	93%	88%	➖
report_submission.migrations	100%	100%	✔
report_submission.templatetags	74%	100%	❌
support	92%	62%	➖
support.management.commands	96%	100%	✔
support.migrations	100%	100%	✔
support.models	97%	83%	✔
tools	98%	50%	✔
users	95%	92%	➖
users.fixtures	100%	83%	✔
users.management	100%	100%	✔
users.management.commands	100%	100%	✔
users.migrations	100%	100%	✔
Summary	91% (17472 / 19297)	76% (2178 / 2860)	➖