fix: always deserialize application_flags in ready event

[shiftinv]

Summary

Trying to access client.application_flags when you created a client with Client(application_id=...) previously resulted in an AttributeError, since the logic was gated by application_id not being set in the first place.

Checklist

• If code changes were made, then they have been tested
  • I have updated the documentation to reflect the changes
  • I have formatted the code properly by running pdm lint
  • I have type-checked the code by running pdm pyright
• This PR fixes an issue
• This PR adds something new (e.g. new method or parameters)
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)