Allow media grid item images to fill container
Allow media grid item images to fill container

See [#5291][0]. Fixes [#5241][1].

[0]: https://github.com/signalapp/Signal-Desktop/pull/5291
[1]: https://github.com/signalapp/Signal-Desktop/issues/5241

nrizzio/Signal-Desktop,nrizzio/Signal-Desktop,nrizzio/Signal-Desktop,nrizzio/Signal-Desktop