Fix potential crash closing Blender with persistent data option enabled

Found by address sanitizer.

source/blender/makesrna/intern/rna_render.c

@@ -298,6 +298,7 @@ static void rna_RenderEngine_unregister(Main *bmain, StructRNA *type)
     return;
   }
 
+  RE_FreeAllPersistentData();
   RNA_struct_free_extension(type, &et->rna_ext);
   RNA_struct_free(&BLENDER_RNA, type);
   BLI_freelinkN(&R_engines, et);