fix: File icons not loading in Safari

Description

• We need to wait for iframe to "load" before writing to it
• gitlab#408414 (closed)

How to test?

• Check out project and run yarn install
• Run yarn start:example
• Open localhost:8000 in Safari
• Enter settings for any GitLab project on .com
• Notice if the file icons show up or not

Screenshots

In Safari:

Before	After