Fix flicker test tool with recent Qt versions
Fix flicker test tool with recent Qt versions

Each call to `...Folder.entryList()` returned a new temporary, so we
called `.begin()` on one and `.end()` on the other.

libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl,libjxl/libjxl