Fix T70522: Sidebars in Clip Editor work incorrectly in Dopesheet mode

Actually, in Dopesheet mode, the regions shouldn't be toggle-able at
all. For the user they should appear to not exist.
Previously the Movie Clip Editor archieved this by setting the region
alignments to NONE, which this restores.

Introduced in 6aef124e7d.

source/blender/makesrna/intern/rna_space.c

@@ -589,7 +589,7 @@ static void rna_Space_bool_from_region_flag_set_by_type(PointerRNA *ptr,
 {
   ScrArea *sa = rna_area_from_space(ptr);
   ARegion *ar = BKE_area_find_region_type(sa, region_type);
-  if (ar) {
+  if (ar && (ar->alignment != RGN_ALIGN_NONE)) {
     SET_FLAG_FROM_TEST(ar->flag, value, region_flag);
   }
   ED_region_tag_redraw(ar);