add pregap support for CHD and CUE

[MetalSlug]

I hope I implemented it correctly. There were no issues during my tests.

[flyinghead]

Why is this needed? Which disk(s) has a pregap?

[MetalSlug]

I fixed this bug in chdman (see mamedev/mame#15808).
In the future, you will be able to create GD-ROM CHDs from CUE files. Redump CHDs include the pregap within the file, whereas TOSEC CHDs feature a virtual pregap.

You can try it with a tosec one and a cue file :

REM SINGLE-DENSITY AREA
FILE "Namco Museum v1.010 (2000)(Namco)(US)[!][2S][compilation] (Track 1).bin" BINARY
TRACK 01 MODE1/2352
INDEX 01 00:00:00
FILE "Namco Museum v1.010 (2000)(Namco)(US)[!][2S][compilation] (Track 2).bin" BINARY
TRACK 02 AUDIO
PREGAP 00:02:00
INDEX 01 00:00:00
REM HIGH-DENSITY AREA
FILE "Namco Museum v1.010 (2000)(Namco)(US)[!][2S][compilation] (Track 3).bin" BINARY
TRACK 03 MODE1/2352
INDEX 01 00:00:00
FILE "Namco Museum v1.010 (2000)(Namco)(US)[!][2S][compilation] (Track 4).bin" BINARY
TRACK 04 AUDIO
PREGAP 00:02:00
INDEX 01 00:00:00
FILE "Namco Museum v1.010 (2000)(Namco)(US)[!][2S][compilation] (Track 5).bin" BINARY
TRACK 05 MODE1/2352
PREGAP 00:04:00
INDEX 01 00:00:00