fix: kyc steps null safety

[xlamn]

• implement null safety check for kycSteps which can ben null and causes requests to be returned with 500.

Release Checklist

Pre-Release

• Check migrations
  • No database related infos (sqldb-xxx)
  • Impact on GS (new/removed columns)
• Check for linter errors (in PR)
• Test basic user operations (on DFX services)
  • Login/logout
  • Buy/sell payment request
  • KYC page

Post-Release

• Test basic user operations
• Monitor application insights log