fix use of dangling pointer #438853
- detail semantics when "cancelling filter manager": either cancel running stroke or cancel the dialog as a whole
- delay deletion / freeing-resources-of
filterDialog
to prevent Qt internals to modify/read this dangling object-pointer - the above was the cause of the segmentation fault reported in #438853
(specifically, Qt's accesibility-update-functions were running due to a
checkbox state update after
d->filterDialog
had been deleted
Edited by Felipe Lema