Fix (studio-reported) crash in ID remapping code on rare cases.

Some ID types did not have a filter value, even though they would be
used in remapping code, leading to missing remappings. In that specific
case, shape keys would actually never be properly remapped.

Reproducible in r1230 of
`Heist/pro/animation_test/einar/einar_new_expression_shapes2.blend`,

source/blender/blenkernel/intern/lib_id_remapper.cc

@@ -36,6 +36,7 @@ struct IDRemapper {
     BLI_assert(old_id != nullptr);
     BLI_assert(new_id == nullptr || (GS(old_id->name) == GS(new_id->name)));
     mappings.add(old_id, new_id);
+    BLI_assert(BKE_idtype_idcode_to_idfilter(GS(old_id->name)) != 0);
     source_types |= BKE_idtype_idcode_to_idfilter(GS(old_id->name));
   }