fix: improve error handling in remotedb package

[vipocenka]

This PR improves error handling in the remotedb package by fixing two issues:

1. In the Has method, we now properly propagate errors instead of silently returning false. This makes the behavior more predictable and helps clients better understand when there are connection issues.

2. In the New constructor, we add a nil check for the client parameter to prevent potential panics. This follows Go best practices for constructor functions.

These changes make the code more robust and follow Go's error handling idioms without requiring any changes to other parts of the codebase.

Changes:

• Modified Has method to return errors instead of silently returning false
• Added nil check in New constructor
• Fixed field name in constructor to match struct definition

[vipocenka]

@MariusVanDerWijden ,
I tested debug_dbGet, and it does not return an error when the key is missing.
It just responds with pebble: not found, which means the key is absent but not an actual error.