Segfault with checkExistingVariable and checkExistingAttribute when export.vars.files.csv-multicols observer is enabled

[crevoisier]

Exception thrown by Engine.cpp checking functions is not catched if required variable or attribute is not present and export.vars.files.csv-multicols observer is enabled.

[Arthoni]

Not able to replicate with basic project, waiting full reproducible example from @crevoisier