fix: display empty image while loading the real one

Author: IvanIhnatsiuk

ios/attachments/ImageAttachment.mm

@@ -8,6 +8,7 @@ - (instancetype)initWithImageData:(ImageData *)data {
     return nil;
 
   _imageData = data;
+  self.image = [UIImage new];
 
   [self loadAsync];
   return self;