[Bug]: Add Error Handling for Empty Records in BloodBankService (blood_bank_service.dart)

[PadmnabhTewari]

Describe the bug

The getBloodBanks method in BloodBankService does not currently handle the case where the API response contains no records or the records field is missing. This could lead to runtime errors or unexpected behavior when the response body is not as expected.

Expected behavior

Without proper error handling, the application may crash or behave unexpectedly if the API response structure changes or if no records are returned.
Add a check to handle cases where data['records'] is null or empty.
Return an appropriate response or an empty list when no records are found.