GUI2/Unit Preview Pane: fixed default race icon not showing for units

Missed in 207e763401. Was only working for unit types.

(cherry-picked from commit f59f68a527)

changelog.md

@@ -50,6 +50,8 @@
  ### User interface
    * Improved the layout of the Statistics dialog.
    * Allow changing dropdown menu selections with the scrollwheel (FR #3251).
+   * Fixed the unit preview pane not showing the default race icon when detailing
+     a single unit's stats.
  ### WML engine
    * Fixed errors about WESNOTH_VERSION not being defined when trying to load
      add-ons that have preprocessor errors (issues #1924, #1634).

src/gui/widgets/unit_preview_pane.cpp

@@ -424,7 +424,7 @@ void unit_preview_pane::set_displayed_unit(const unit& u)
 	}
 
 	if(icon_race_) {
-		icon_race_->set_label("icons/unit-groups/race_" + u.race()->id() + "_30.png");
+		icon_race_->set_label(u.race()->get_icon_path_stem() + "_30.png");
 	}
 
 	if(icon_alignment_) {