message: [terminal_renderer] Renderer: Adds ability to test for existence of a RenderTarget.
diff: @@ -75,6 +75,7 @@ class Renderer
  /// and then informs all renderables about the newly created texture atlas.
  void setRenderTarget(RenderTarget& renderTarget);
  RenderTarget& renderTarget() noexcept { return *_renderTarget; }
  + bool hasRenderTarget() const noexcept { return _renderTarget != nullptr; }
  void setBackgroundOpacity(terminal::Opacity _opacity) { backgroundOpacity_ = _opacity; }
  terminal::Opacity backgroundOpacity() const noexcept { return backgroundOpacity_; }
  