Fixed SpriteBatch:unbind

src/modules/graphics/opengl/VertexBuffer.h

@@ -106,6 +106,11 @@ public:
 		return usage;
 	}
 
+	bool isBound() const
+	{
+		return is_bound;
+	}
+
 	/**
 	 * Map the VertexBuffer to client memory.
 	 *
@@ -222,6 +227,11 @@ public:
 		void *elems;
 	};
 
+protected:
+
+	// Whether the buffer is currently bound.
+	bool is_bound;
+
 private:
 
 	// The size of the buffer, in bytes.