For contentless cores like 2048 and the retropad RetroArch will save png
files with the content field missing.
-181227-133151.png
Now RetroArch will save png files with the correct names for contentless
cores.
2048-181227-133151.png
RetroPad Remote-181227-133202.png
Cores with content will have no change in behavior.
Akumajou Dracula (J)-181227-133232.png
And with cores that support content and no content such as 4DO both
variations will work.
4DO-181227-144102.png
LuciennesQuest-181227-144118.png
Fixes https://github.com/libretro/RetroArch/issues/7828