Primitives: fix an assertion in uvSphereWireframe().

Everything I do these days is a potential breakign change.

doc/changelog.dox

@@ -156,6 +156,10 @@ See also:
     @ref Platform::Sdl2Application now premultiply the value with
     @ref Platform::GlfwApplication::dpiScaling() "dpiScaling()" to work
     independently on display DPI. This might break existing uses.
+-   @ref Primitives::uvSphereWireframe() now correctly asserts when the
+    @p segments parameter isn't divisible by four. Before it mistakenly
+    asserted only if @p segments wasn't divisible by two, and now code that
+    mistakenly used a disallowed value will start asserting.
 -   Removed remaining APIs deprecated in version 2018.04:
     -   @cpp Audio::Buffer::Format @ce, use @ref Audio::BufferFormat instead
     -   @cpp Shaders::*Vector::setVectorTexture() @ce,

src/Magnum/Primitives/UVSphere.cpp

@@ -63,7 +63,7 @@ Trade::MeshData3D uvSphereSolid(UnsignedInt rings, UnsignedInt segments, UVSpher
 }
 
 Trade::MeshData3D uvSphereWireframe(const UnsignedInt rings, const UnsignedInt segments) {
-    CORRADE_ASSERT(rings >= 2 && rings%2 == 0 && segments >= 4 && segments%2 == 0,
+    CORRADE_ASSERT(rings >= 2 && rings%2 == 0 && segments >= 4 && segments%4 == 0,
         "Primitives::uvSphereWireframe(): multiples of 2 rings and multiples of 4 segments expected",
         (Trade::MeshData3D{MeshPrimitive::Triangles, {}, {}, {}, {}, {}, nullptr}));