MeshTools: fix a bad corner case in compile().

Having texture coordinates *and* colors is very unusual, nevertheless it
was a bug.

doc/changelog.dox

@@ -297,6 +297,8 @@ See also:
     (see [mosra/magnum#331](https://github.com/mosra/magnum/pull/331)
 -   Reading of float textures on ES3 contexts using
     @ref DebugTools::textureSubImage() returned a zero-sized image by accident
+-   @ref MeshTools::compile() was producing an incorrect mesh when
+    @ref Trade::MeshData3D had both colors and texture coordinates
 -   Properly zero-initializing the UTF-8 buffer in
     @ref Platform::GlfwApplication::textInputEvent() (see
     [mosra/magnum#324](https://github.com/mosra/magnum/pull/324))

src/Magnum/MeshTools/Compile.cpp

@@ -137,7 +137,7 @@ GL::Mesh compile(const Trade::MeshData3D& meshData) {
     }
     if(meshData.hasTextureCoords2D()) {
         stride += sizeof(Shaders::Generic3D::TextureCoordinates::Type);
-        colorsOffset += sizeof(Shaders::Generic3D::Normal::Type);
+        colorsOffset += sizeof(Shaders::Generic3D::TextureCoordinates::Type);
     }
     if(meshData.hasColors())
         stride += sizeof(Shaders::Generic3D::Color4::Type);