Fix T78837: Prefetching can corrupt .blend files

This happened because of typo in seq_dupli() when duplicating effect data.
Instead of duplicating data to new sequence, it was duplicated into original.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8295

source/blender/blenkernel/intern/sequencer.c

@@ -5725,7 +5725,7 @@ static Sequence *seq_dupli(const Scene *scene_src,
     struct SeqEffectHandle sh;
     sh = BKE_sequence_get_effect(seq);
     if (sh.copy) {
-      sh.copy(seq, seqn, flag);
+      sh.copy(seqn, seq, flag);
     }
 
     seqn->strip->stripdata = NULL;