gui2/unit_create: Use variation_name before the variation's ut name

Forgot that variation_name has an actual meaning when paired with
variation_id as opposed to it just being a deprecated form of
variation_id. This makes it so it's favoured by the UI over a
potentially overridden type name when present.

This makes it so the mainline Walking Corpse and Soulless units have
their translatable variation names properly displayed.

src/gui/dialogs/unit_create.cpp

@@ -240,7 +240,9 @@ void unit_create::list_item_clicked(window& window)
 		const unit_type& uv = pair.second;
 
 		std::string uv_label;
-		if(!uv.type_name().empty() && uv.type_name() != ut.type_name()) {
+		if(!uv.variation_name().empty()) {
+			uv_label = uv.variation_name() + " (" + uv_id + ")";
+		} else if(!uv.type_name().empty() && uv.type_name() != ut.type_name()) {
 			uv_label = uv.type_name() + " (" + uv_id + ")";
 		} else {
 			uv_label = uv_id;