Create box for image before it loads.

[Qwertie-]

Currently nheko reserves no space for images which causes the chat window to jump around as images load. By the looks of it the image dimensions/ratio can be seen before the image is downloaded so creating a box in the same ratio as the image before the image has loaded would mean the chat doesn't move when images load.

[mujx]

Just a note that message event that contains the image isn't guaranteed to contain the size information.

The flickering issue could be adjusted in other ways.

[vurpo]

Is there a separate issue for the jumping around issue? It makes it really hard to use image-heavy rooms.

[mujx]

@vurpo The jumping around issue is related to the widget changing size, so I think this issue will handle it.