Improve network table error handling

[DL6ER]

What does this implement/fix?

Go through network-table.c and ensure error handling is uniform, there were some cases in which an early returning caused by an error could have left prepared SQLite3 statements un-finalized. Whether this is the cause for occasional database locking we are seeing is unclear. However, the change

is specifically tailored to fix the cause of recently reported ERROR: add_netDB_network_address(-1, "192.168.0.168"): Failed to step (error 19): constraint failed messages.

---

Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): N/A

---

By submitting this pull request, I confirm the following:

1. I have read and understood the contributors guide, as well as this entire template. I understand which branch to base my commits and Pull Requests against.
2. I have commented my proposed changes within the code.
3. I am willing to help maintain this change if there are issues with it later.
4. It is compatible with the EUPL 1.2 license
5. I have squashed any insignificant commits. (git rebase)

Checklist:

• The code change is tested and works locally.
• I based my code and PRs against the repositories developmental branch.
• I signed off all commits. Pi-hole enforces the DCO for all contributions
• I signed all my commits. Pi-hole requires signatures to verify authorship
• I have read the above and my PR is ready for review.

[DL6ER]

Seems to be working:

• https://discourse.pi-hole.net/t/network-overview/73630/8
• https://discourse.pi-hole.net/t/database-locked-in-newest-beta-v6-0-no-clients-listed/73624/11