fix: preserve help request edit location prefill

[delibas-rojhat]

Summary

• Preserves existing Request Help location fields when a remote refresh returns partial location data
• Prevents edit forms from opening with blank country/city/district/neighborhood/extra address values
• Adds regression coverage for preserving address fields and coordinates during remote mapping

Closes #615

[AlperKartkaya]

This PR successfully
- Fixes a different root cause in RequestHelpRepository.kt.
- Preserves existing local location fields when the backend returns a partial/empty location object.
- Adds a repository mapping regression test.

LGTM.