Fix (unreported) memory leak when freeing Master collections.

Potential ID properties there (or any other ID data itself) would not be
freed.

source/blender/blenkernel/intern/collection.c

@@ -474,6 +474,7 @@ void BKE_collection_add_from_collection(Main *bmain,
 /** Free (or release) any data used by this collection (does not free the collection itself). */
 void BKE_collection_free(Collection *collection)
 {
+  BKE_libblock_free_data(&collection->id, false);
   collection_free_data(&collection->id);
 }