make video cells square if content has not been loaded

deltachat-ios/MessageKit/Layout/MediaMessageSizeCalculator.swift

@@ -31,8 +31,6 @@ open class MediaMessageSizeCalculator: MessageSizeCalculator {
         return UIScreen.main.bounds.size.height * 0.7
     }
 
-    private let defaultHeight: CGFloat = 350
-
     open override func messageContainerSize(for message: MessageType) -> CGSize {
         let maxWidth = messageContainerMaxWidth(for: message)
         let sizeForMediaItem = { (maxWidth: CGFloat, item: MediaItem) -> CGSize in
@@ -58,7 +56,7 @@ open class MediaMessageSizeCalculator: MessageSizeCalculator {
         case .video(let item):
             if item.image == nil {
                 // no cached thumbnail -> is generated asynchronously
-                return CGSize(width: maxWidth, height: defaultHeight)
+                return CGSize(width: maxWidth, height: maxWidth)
             } else {
                 return sizeForMediaItem(maxWidth, item)
             }