Renderer: solve a Javadoc warning

jme3-core/src/main/java/com/jme3/renderer/Renderer.java

@@ -262,6 +262,7 @@ public interface Renderer {
      *
      * @param unit the index of the texture unit (≥0)
      * @param tex the Texture to assign
+     * @throws TextureUnitException if the texture unit doesn't exist
      */
     public void setTexture(int unit, Texture tex)
             throws TextureUnitException;