fix: inverse condition following cppcheck advice
fix: inverse condition following cppcheck advice

untereiner/CGoGN_2,cgogn/CGoGN_2,david-cazier/CGoGN_2,david-cazier/CGoGN_2,cgogn/CGoGN_2,untereiner/CGoGN_2,etienneschmitt/CGoGN_2