Updated "unsaved" favorite icon with an empty icon to make it more clear

[JakeShirley]

Checklist

• [x] I have described what this PR contains

Choose one of the following two options:

• • [x] This PR does not introduce major changes
• • [ ] This PR introduces major changes, and I have consulted the Mlem Development Matrix room

Choose one of the following two options:

• • [ ] This PR does not change the UI in any way
• • [x] This PR adds new UI elements / changes the UI, and I have attached pictures or videos of the new / changed UI elements

Pull Request Information

About this Pull Request

Updates the unfavorited icon to be unfilled to make it clearer which state it is in.

Screenshots and Videos

Additional Context

Resolves #282