fix: skip empty object write for untouched localized fields in mergeLocalizedData

[deepshekhardas]

Description

When \mergeLocalizedData\ encounters untouched localized fields (fields that haven't been modified), it was writing empty objects {}\ into the database instead of skipping them entirely. This caused data loss in specific scenarios where partial updates were performed on localized documents.

Root Cause

The \mergeLocalizedData\ utility in the payload core was not checking if the incoming value for a localized field was an empty object before proceeding with the write. An empty object {}\ vs \undefined/null makes a difference in how the database handles the field - empty objects overwrite existing localized data.

Fix

Added a guard to skip writing when the incoming value for a localized field is an empty object {}. This ensures untouched fields retain their existing values.

Note

This PR was split from an earlier combined PR. The related fixes are now in separate PRs:

• Connection leak fix: fix(db-postgres): release connection back to pool in connectWithReconnect #16893
• Unicode regex fix: fix(drizzle): allow unicode characters in JSON query values #16894

Type of change

• Bug fix (non-breaking change which fixes an issue)