Fix T77669: Copy-pasting strip twice crashes Blender

In rBeaee2b411935 I removed BKE_sequencer_base_clipboard_pointers_store from
paste function, because I wanted pasted strip to always reference copied
strip, not recently pasted one. This worked well with ordinary strips, but not
if they reference ID.

Add back BKE_sequencer_base_clipboard_pointers_store call.

I thought that always referencing original strip would be more correct approach,
but it doesn't matter now. Referencing recently pasted seems to be cleanest way
to do this.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D8129

source/blender/editors/space_sequencer/sequencer_edit.c

@@ -3453,6 +3453,7 @@ static int sequencer_paste_exec(bContext *C, wmOperator *UNUSED(op))
    * on the actual data-blocks. */
   BKE_sequencer_base_clipboard_pointers_restore(&seqbase_clipboard, bmain);
   BKE_sequence_base_dupli_recursive(scene, scene, &nseqbase, &seqbase_clipboard, 0, 0);
+  BKE_sequencer_base_clipboard_pointers_store(bmain, &seqbase_clipboard);
 
   iseq_first = nseqbase.first;