Fall back to the unit type name for [message] captions for nameless units

Fixes #3211.

(cherry-picked from commit 051182fa1c)

changelog.md

@@ -232,6 +232,8 @@
      access of the image cache.
    * [kill] animate=yes no longer scrolls to units through fog or shroud, thus
      matching 1.12's behavior again.
+   * [message] displays the unit type name when a nameless unit speaks and no
+     custom caption= is specified (fixes #3211).
 
 ## Version 1.13.12
  ### Security fixes

data/lua/wml/message.lua

@@ -42,7 +42,11 @@ local function get_caption(cfg, speaker)
 	local caption = cfg.caption
 
 	if not caption and speaker ~= nil then
-		caption = speaker.name or speaker.type_name
+		if speaker.name ~= nil and tostring(speaker.name):len() > 0 then
+			caption = speaker.name
+		else
+			caption = speaker.__cfg.language_name
+		end
 	end
 
 	return caption