Parsing fails with non-standard APP0

Some JPEGs have a non-standard APP0 segment. It is non-standard but it breaks parsing because jay-peg assumes fixed size APP0.

I can't give the original image but here's the hex for the broken segment: (includes APP0 marker, two-byte size, and the whole marker data)

```0xFF,0xE0,0x00,0x14,0x4A,0x46,0x49,0x46,0x00,0x01,0x01,0x01,0x01,0x2C,0x01,0x2C,0x00,0x00,0x41,0x4D,0x50,0x46```

The last four bytes spell out `AMPF` in ascii, which according to a [random googling](https://exiftool.org/forum/index.php?topic=12677.0) is somehow related to some Apple extension. See also https://github.com/exiftool/exiftool/blob/master/lib/Image/ExifTool.pm#L2226

Start by tracing jay-peg's APP0 parsing entry point and reproduce the failure with the hexadecimal segment in the issue. The fix is done when this non-standard APP0 segment, including its declared size and trailing AMPF bytes, parses without breaking JPEG decoding.

Written by the indexing model from the issue text.