Favicon downloader should ignore unmodified icons

[keepassium]

Description
Favicon downloading is always processed as an update, even if all the icons have remained the same (e.g. in a repeated call).

How to reproduce

1. Create a database with some sample entries and URLs set to sites with favicons.
2. Tap Tools → Download Favicons → confirm the warning
3. Observe message "Entries processed: M, Icons updated: N"
4. Repeat step 2
5. Observe the same message, with N the same as in step 3, even though all the favicons have remained the same. (And custom icon list successfully skipped the duplicates.)
6. Check history of any updated entry: there is a snapshot for every call of favicon downloader, even though the entry has not changed (nor its custom icon).

Expected behavior
Non-changed favicons should be ignored: not included in "icons updated" counter, nor create a historical entry.

Environment:

• Device: any
• App Version: 2.5.171

[thanks, Alex]