Bug Fix - Chat screen: image thumbnails management is broken

element-hq/element-ios#1121

The thumbnail url was computed before retrieving the content url. The resulting url was nil.

MatrixKit/Models/Room/MXKAttachment.m

@@ -118,9 +118,6 @@ - (instancetype)initWithEvent:(MXEvent *)mxEvent andMatrixSession:(MXSession*)mx
 
         thumbnailFile = _contentInfo[@"thumbnail_file"];
 
-        _thumbnailURL = [self getThumbnailUrlForSize:CGSizeMake(kThumbnailWidth, kThumbnailHeight)];
-        _thumbnailMimeType = [self getThumbnailMimeType];
-
         contentFile = eventContent[@"file"];
 
         // Retrieve the content url by taking into account the potential encryption.
@@ -155,6 +152,10 @@ - (instancetype)initWithEvent:(MXEvent *)mxEvent andMatrixSession:(MXSession*)mx
         }
 
         _cacheFilePath = [MXMediaManager cachePathForMediaWithURL:_actualURL andType:mimetype inFolder:_eventRoomId];
+
+        // Deduce the thumbnail information from the retrieved data.
+        _thumbnailURL = [self getThumbnailUrlForSize:CGSizeMake(kThumbnailWidth, kThumbnailHeight)];
+        _thumbnailMimeType = [self getThumbnailMimeType];
     }
     return self;
 }