"Never happened" seems a bit much, but in the end, it doesn't seem hard to have the "Scramble for Africa" resulting in only some trading posts and a bunch of indigenous client states of European nations. Just have European nations not seek much more out of Africa other than shutting down the Transatlantic slave trade and in general, trade with the continent.
Africa would be a mixed bunch compared to today. There'd be many regions with GDPs 3-5 times higher, but other regions very comparable to OTL's economic development.
Europe wouldn't have to sink huge amounts of income into maintaining colonial garrisons, fighting colonial wars, etc., and most African colonies never turned a profit for Europeans anyway.
Well, the continent can be viewed as inhospitable to "civilized" life. Get enough people to bleeive it and it's a self fulfilloing prosphecy
And explorers and missionaries, who paved the way for European dominance, can prove that blatantly false, in large part because of new-fangled European medicine (quinine, etc.). And why would Europeans be afraid of uncivilised people with all their new military technology?