Flush cache before normalizing block

`normalize_block()` was unable to find newly inserted resources (for instance, during `manage_schema()`). This commit fixes that by flushing the cache before the `m_rsc:rid()` lookups that were introduced with 357f0bbc26925002f1c005a16dfdc0b83a9bd0dc.

Please backport this to release-0.10.x.