footage: merge video type

Fixes issue where image sequences would revert to stills after a project is loaded

app/node/project/footage/footage.cpp

@@ -512,6 +512,7 @@ VideoParams Footage::MergeVideoStream(const VideoParams &base, const VideoParams
   merged.set_interlacing(over.interlacing());
   merged.set_colorspace(over.colorspace());
   merged.set_premultiplied_alpha(over.premultiplied_alpha());
+  merged.set_video_type(over.video_type());
   if (merged.video_type() == VideoParams::kVideoTypeImageSequence && over.video_type() == VideoParams::kVideoTypeImageSequence) {
     merged.set_start_time(over.start_time());
     merged.set_duration(over.duration());