== Sequencer ==

This fixes:
[#11745] Blender crashes when changing Scenes on Sequencer`s Strips

containing:

- last_seq was set to null by scene-render
- button handling wasn't very robust (didn't check for null)
- REDRAWBUTSSCENE was missing

source/blender/src/buttons_scene.c

@@ -1286,6 +1286,10 @@ void do_sequencer_panels(unsigned short event)
 	Sequence *last_seq = get_last_seq();
 	ScrArea * sa;
 
+	if (!last_seq) {
+		return;
+	}
+
 	switch(event) {
 	case B_SEQ_BUT_PLUGIN:
 	case B_SEQ_BUT_EFFECT:
@@ -1323,6 +1327,7 @@ void do_sequencer_panels(unsigned short event)
 		allqueue(REDRAWALL, 0);
 	} else {
 		allqueue(REDRAWSEQ, 0);
+		allqueue(REDRAWBUTSSCENE, 0);
 	}
 }
 

source/blender/src/sequence.c

@@ -1756,6 +1756,7 @@ static void do_build_seq_ibuf(Sequence * seq, TStripElem *se, int cfra,
 		}
 	} else if(seq->type == SEQ_SCENE) {	// scene can be NULL after deletions
 		int oldcfra = CFRA;
+		Sequence * oldseq = get_last_seq();
 		Scene *sce= seq->scene, *oldsce= G.scene;
 		Render *re;
 		RenderResult rres;
@@ -1834,6 +1835,7 @@ static void do_build_seq_ibuf(Sequence * seq, TStripElem *se, int cfra,
 			if((G.f & G_PLAYANIM)==0) /* bad, is set on do_render_seq */
 				waitcursor(0);
 			CFRA = oldcfra;
+			set_last_seq(oldseq);
 
 			copy_to_ibuf_still(seq, se);