fix: resume worldmap music when naving back from game scene

Was stopping music too aggressively here. of note - the next scene's
_ready fires before the current scene's _exit_tree! wut!

src/menus/worldmap/WorldMapMenu.gd

@@ -22,7 +22,7 @@ var current_puzzle_index = 0
 
 func _ready():
 	if not Engine.is_editor_hint():
-		SoundManager.play_music(Music.late_night_radio)
+		SoundManager.play_music(Music.late_night_radio, 2.0)
 		reset_map()
 
 	var next_to_complete_puzzle_idx = 0

src/puzzle/GameScene.gd

@@ -42,7 +42,11 @@ func _ready():
 			SoundManager.play_music(song, 2.0)
 
 func _exit_tree():
-	SoundManager.stop_music(2.0)
+	var song = puzzle_theme.get_background_music()
+	var songs = SoundManager.get_currently_playing_music()
+	if len(songs) == 1:
+		if songs[0] == song:
+			SoundManager.stop_music(2.0)
 
 func nav_to_world_map():
 	# TODO better navigation (string-less, path-less)