Editor: 'unhide' palette when drawing contents

I'm not sure why, but this allows the enabled state of the to be set properly when switching to a tool
with an empty palette. It seems this function is called after editor_toolkit::hotkey_set_mouse_action
is fired, which already seems to do that, so I'm not sure why it doesn't take effect there, but meh.

Also includes a fixup for when palette_menu_button is fetched. It's a menu button not an action button,
but it probably not havig worked before seems not to have affected anything.

src/editor/palette/palette_manager.cpp

@@ -136,14 +136,14 @@ void palette_manager::draw_contents()
 	std::shared_ptr<gui::button> downscroll_button = gui_.find_action_button("downscroll-button-editor");
 	if (downscroll_button)
 		downscroll_button->hide(false);
-	std::shared_ptr<gui::button> palette_menu_button = gui_.find_action_button("menu-editor-terrain");
+	std::shared_ptr<gui::button> palette_menu_button = gui_.find_menu_button("menu-editor-terrain");
 	if (palette_menu_button)
 		palette_menu_button->hide(false);
 
 //	bg_restore(loc);
 	active_palette().set_dirty(true);
+	active_palette().hide(false);
 	active_palette().draw();
-	//active_palette().hide(false);
 
 //	set_dirty(false);
 }