From e68bdd1b5f479da2c1c0e1144cc4dbce1498bb44 Mon Sep 17 00:00:00 2001
From: Iris Morelle <shadowm@wesnoth.org>
Date: Sat, 9 Jun 2018 18:53:18 -0400
Subject: [PATCH] Fix Lua errors when failing to set a music track on an empty
 playlist

Closes #3194.

(cherry-picked from commit 5871557dbfe407ab454d9f55be6bc2a0fcad0434)
---
 changelog.md          |  3 +++
 data/lua/wml-tags.lua | 10 ++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/changelog.md b/changelog.md
index 62ab350a5b5c..fd31dcd8eaee 100644
--- a/changelog.md
+++ b/changelog.md
@@ -245,6 +245,9 @@
      be initially selected in the Unit Attack dialog. This bug also had the
      potential to cause units to the wrong attack when  engaging or viewing
      damage calculations.
+   * Fixed Lua errors when setting a music track that cannot be found when the
+     playlist is already empty, e.g. if there's no music installed for the
+     game (issue #3194).
 
 ## Version 1.13.12
  ### Security fixes
diff --git a/data/lua/wml-tags.lua b/data/lua/wml-tags.lua
index 159c76c9ae89..fe4a4139b879 100644
--- a/data/lua/wml-tags.lua
+++ b/data/lua/wml-tags.lua
@@ -277,17 +277,23 @@ function wml_actions.music(cfg)
 		wesnoth.music_list.play(cfg.name)
 	else
 		if not cfg.append then
-			if cfg.immediate then
+			if cfg.immediate and wesnoth.music_list.current_i then
 				wesnoth.music_list.current.once = true
 			end
 			wesnoth.music_list.clear()
 		end
+		local m = #wesnoth.music_list
 		wesnoth.music_list.add(cfg.name, not not cfg.immediate, cfg.ms_before or 0, cfg.ms_after or 0)
 		local n = #wesnoth.music_list
+		if n == 0 then
+			return
+		end
 		if cfg.shuffle == false then
 			wesnoth.music_list[n].shuffle = false
 		end
-		if cfg.title ~= nil then
+		-- Always overwrite shuffle even if the new track couldn't be added,
+		-- but title shouldn't be overwritten.
+		if cfg.title ~= nil and m ~= n then
 			wesnoth.music_list[n].title = cfg.title
 		end
 	end