U.S. IPO activity is stuck in a troubling rut —see: WeWork’s spectacular implosion—and that could jeopardize initial public offerings for both Madewell and Old Navy. Over the course of 2019, several fashion brands and e-retailers have completed initial public offerings, including Levi Strauss & Co., Kontoor Brands Inc., Revolve Group Inc. and The RealReal Inc. But…