Fix rare appleseed.studio crash when quickly stopping then restarting a render
Fix rare appleseed.studio crash when quickly stopping then restarting a render

est77/appleseed,Biart95/appleseed,luisbarrancos/appleseed,Vertexwahn/appleseed,luisbarrancos/appleseed,Biart95/appleseed,pjessesco/appleseed,Vertexwahn/appleseed,appleseedhq/appleseed,est77/appleseed,appleseedhq/appleseed,Vertexwahn/appleseed,dictoon/appleseed,dictoon/appleseed,luisbarrancos/appleseed,est77/appleseed,appleseedhq/appleseed,appleseedhq/appleseed,est77/appleseed,Biart95/appleseed,dictoon/appleseed,Biart95/appleseed,pjessesco/appleseed,pjessesco/appleseed,Vertexwahn/appleseed,pjessesco/appleseed,est77/appleseed,dictoon/appleseed,Vertexwahn/appleseed,Biart95/appleseed,luisbarrancos/appleseed,pjessesco/appleseed,dictoon/appleseed,luisbarrancos/appleseed,appleseedhq/appleseed