Fix the simpleRootAreaProvider following 4fa0b6e29
The commit 4fa0b6e29d31d7755441b231ea3bf2ef068435b4 introduced a refactoring of KoTextDocumentLayout that required doing the caching of rootAreas at the provider level. A failure to do so led to weird behaviours like missing inputs, missing rendering and so on in stage and other applications. Thanks to leinir for reporting the issue.
Showing with 5 additions and 2 deletions