DebugTools: don't use CORRADE_INTERNAL_ASSERT() for user-triggered error.

What was I thinking... Also updated the documentation to warn about it.

src/DebugTools/ShapeRenderer.cpp

@@ -68,7 +68,7 @@ template<> void createDebugMesh(ShapeRenderer<3>* renderer, Physics::AbstractSha
 #endif
 
 template<std::uint8_t dimensions> ShapeRenderer<dimensions>::ShapeRenderer(Physics::ObjectShape<dimensions>* shape, ResourceKey options, SceneGraph::DrawableGroup<dimensions>* drawables): SceneGraph::Drawable<dimensions>(shape->object(), drawables), options(ResourceManager::instance()->get<ShapeRendererOptions>(options)) {
-    CORRADE_INTERNAL_ASSERT(shape->shape() != nullptr);
+    CORRADE_ASSERT(shape->shape() != nullptr, "DebugTools::ShapeRenderer: cannot create renderer for empty shape", );
     Implementation::createDebugMesh(this, shape->shape());
 }
 

src/DebugTools/ShapeRenderer.h

@@ -90,7 +90,7 @@ template<std::uint8_t dimensions> class MAGNUM_DEBUGTOOLS_EXPORT ShapeRenderer:
     public:
         /**
          * @brief Constructor
-         * @param shape     Shape for which to create debug renderer
+         * @param shape     Object for which to create debug renderer
          * @param options   Options resource key. See
          *      @ref ShapeRenderer-usage "class documentation" for more
          *      information.
@@ -98,6 +98,8 @@ template<std::uint8_t dimensions> class MAGNUM_DEBUGTOOLS_EXPORT ShapeRenderer:
          *
          * The renderer is automatically added to shape's object features,
          * @p shape must be available for the whole lifetime of the renderer.
+         *
+         * @attention Passed object must have assigned shape.
          */
         explicit ShapeRenderer(Physics::ObjectShape<dimensions>* shape, ResourceKey options = ResourceKey(), SceneGraph::DrawableGroup<dimensions>* drawables = nullptr);