Fix T39018: Duplicate entries for material/shader in AnimEditors

In many BI shader setups, the material which owns the nodetree is often itself
included as a node in that nodetree (i.e. to provide the base colour for that
mesh). This would often result in the material (and its subtree) getting included
in the dopesheet results twice.

source/blender/editors/animation/anim_filter.c

@@ -1796,9 +1796,14 @@ static size_t animdata_filter_ds_materials(bAnimContext *ac, ListBase *anim_data
 			Material *base = give_current_material(ob, a);
 			Material *ma   = give_node_material(base);
 			
-			/* add channels from the nested material if it exists */
-			if (ma)
+			/* add channels from the nested material if it exists
+			 *   - skip if the same material is referenced in its node tree
+			 *     (which is common for BI materials) as that results in
+			 *     confusing duplicates
+			 */
+			if ((ma) && (ma != base)) {
 				items += animdata_filter_ds_material(ac, anim_data, ads, ma, filter_mode);
+			}
 		}
 	}