renderer: fixed distorted video caused by exporting video with lower frame rate than sequence

Wow I thought this issue was 0.1 exclusive but the same bug was here in 0.2 I wonder if it's worth backporting it now that I know what the problem is.

app/task/export/export.cpp

@@ -163,7 +163,7 @@ void ExportTask::FrameDownloaded(FramePtr f, const QByteArray &hash, const QVect
 
   forever {
     rational real_time = Timecode::timestamp_to_time(frame_time_,
-                                                     viewer()->GetVideoParams().frame_rate_as_time_base());
+                                                     video_params().frame_rate_as_time_base());
 
     if (!time_map_.contains(real_time)) {
       break;

app/task/render/render.cpp

@@ -76,7 +76,7 @@ bool RenderTask::Render(ColorManager* manager,
 
   if (!video_range.isEmpty()) {
     // Get list of discrete frames from range
-    QVector<rational> times = viewer()->video_frame_cache()->GetFrameListFromTimeRange(video_range);
+    QVector<rational> times = FrameHashCache::GetFrameListFromTimeRange(video_range, video_params().frame_rate_as_time_base());
     QVector<QByteArray> hashes(times.size());
 
     // Generate hashes