Properly specify pointers for all matrix attribute columns.

Really need some tests for that.

src/Mesh.h

@@ -660,10 +660,10 @@ class MAGNUM_EXPORT Mesh {
                     offset,
                     stride
                 });
-            }
 
                 (this->*attributePointerImplementation)(attributes.back());
             }
+        }
 
         #ifndef MAGNUM_TARGET_GLES2
         template<GLuint location, class T> inline void addVertexAttribute(typename std::enable_if<std::is_integral<typename Implementation::AttributeTraits<T>::AttributeType>::value, Buffer*>::type buffer, const AbstractShaderProgram::Attribute<location, T>& attribute, GLintptr offset, GLsizei stride) {