Adding magic number for iso saturn cds scan

[i30817]

[Description of the bug]

On this line https://github.com/libretro/RetroArch/blob/master/tasks/task_database_cue.c#L59 the scanner whitelists the recognized content files. I believe that there is a 'missing' content file for saturn cd iso. The 3rd one is for sega cd bins, but conversion to iso lops off part of the header (everything before SEGASEGASATURN.

While it could be argued that redump is all in cue/bins, the reason why this is important is to pick up content files from hardpatch translations and hacks. Many of them have a intermediate step of 'convert to MODE1/2048' in order to have a smaller size for the patch. While beetle saturn doesn't support isos, it does support cue files with a data track of MODE1/2048, which is the same.

[What you expected to happen]

The scanner would at least try to scan the content file after finding a .cue file pointing to a iso.

[What is actually happening]

1. Scan a hardpatched translation that does this 'convert to MODE1/2048' to a Saturn game, for example Dragon Force II:

    		RetroArch [INFO] :: Parsing CUE file '/media/i30817/backup/Documents/Games/Sega Saturn/Dragon Force II - Kami Sarishi Daichi ni (Japan)/Dragon Force II - Kami Sarishi Daichi ni (Japan) [ISO].cue'...
    		RetroArch [INFO] :: Found first data track on file '/media/i30817/backup/Documents/Games/Sega Saturn/Dragon Force II - Kami Sarishi Daichi ni (Japan)/Dragon Force II - Kami Sarishi Daichi ni (Japan) (Track 1).iso+0'
    		RetroArch [INFO] :: Reading first data track...
    		RetroArch [INFO] :: Comparing with known magic numbers...
    		RetroArch [INFO] :: Could not find compatible system.
   

Even my non-patched redump saturn games aren't being picked up for another reason i didn't figure out yet (they don't add to a playlist); but this one is another (obvious) bug.

[i30817]

Thinking about it, this isn't different from ps1 translations that need iso, that are few and far between now (i can't think of a single one, Policenauts says it needs a iso, but it uses redump and outputs MODE2/2352 like all the rest), probably because redump applying pressure to use it as source and the console using that data.

I do not know if the Saturn uses the ECD or not, so i don't know that the translations will try to target a MODE1/2532 dump (redump uses this for the saturn set) or not. It's a question if burning a iso to cd can work on the hardware or not, and that's a little after my time.