Custom icons for the same website are added multiple times.

Expected Behavior

We should at least try to detect duplicates and not fetch the icon multiple times for the same website.

Current Behavior

Custom icons for the same website are added multiple times.

Steps to Reproduce (for bugs)

1. Add entry with a website
2. Click Download favicon multiple times.

Context

I was trying to reproduce #225

Your Environment

• KeePassXC version/commit used: 6409661
• Qt version: Qt 5.7.1
• Operating System and version: MacOS 10.11.16