fixes crash when spriters credits list is malformatted

Data/Scripts/050_AddOns/SpriteCreditsUtils.rb

@@ -3,11 +3,13 @@ def map_sprites_by_artist
   File.foreach(Settings::CREDITS_FILE_PATH) do |line|
     row = line.split(',')
     spritename = row[0]
+    if row[1]
       artist = row[1].chomp
       sprites = creditsMap.key?(artist) ? creditsMap[artist] : []
       sprites << spritename
       creditsMap[artist] = sprites
     end
+  end
   return creditsMap
 end