[fix][fn] Only load crypto_key_reader for python function when cryptoKeyReaderConfig is provided

[jiangpengcheng]

Fixes #24782

Motivation

The python function will try to load crypto_config from crypto_spec.cryptoKeyReaderConfig even it's empty or None, which will show an un-expected error log Failed to load the crypto key reader from spe

Modifications

check the crypto_spec.cryptoKeyReaderConfig before load it

Verifying this change

• Make sure that the change passes the CI checks.

• This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: jiangpengcheng#48