Primitives: test for circle mesh primitive as well.

So I see what's looping and what not.

src/Magnum/Primitives/Test/CircleTest.cpp

@@ -25,6 +25,7 @@
 
 #include <Corrade/TestSuite/Tester.h>
 
+#include "Magnum/Mesh.h"
 #include "Magnum/Math/Vector2.h"
 #include "Magnum/Primitives/Circle.h"
 #include "Magnum/Trade/MeshData2D.h"
@@ -46,6 +47,7 @@ CircleTest::CircleTest() {
 void CircleTest::solid() {
     Trade::MeshData2D circle = Primitives::Circle::solid(8);
 
+    CORRADE_COMPARE(circle.primitive(), MeshPrimitive::TriangleFan);
     CORRADE_COMPARE(circle.positions(0), (std::vector<Vector2>{
         { 0.0f,  0.0f},
         { 1.0f,  0.0f}, { Constants::sqrt2()/2.0f,  Constants::sqrt2()/2.0f},
@@ -59,6 +61,7 @@ void CircleTest::solid() {
 void CircleTest::wireframe() {
     Trade::MeshData2D circle = Primitives::Circle::wireframe(8);
 
+    CORRADE_COMPARE(circle.primitive(), MeshPrimitive::LineLoop);
     CORRADE_COMPARE(circle.positions(0), (std::vector<Vector2>{
         { 1.0f,  0.0f}, { Constants::sqrt2()/2.0f,  Constants::sqrt2()/2.0f},
         { 0.0f,  1.0f}, {-Constants::sqrt2()/2.0f,  Constants::sqrt2()/2.0f},