Handle MotionPhoto JPEG files with embedded video

[gkv311]

There are JPEG files called 'MotionPhoto', which store video inside. It would be useful to support reading this video stream.
At minimum, it is necessary to fix issues in JPEG parser that lead to misdetection of such files.

exiftool -b -EmbeddedVideoFile my_motion_photo.jpg >video.mp4

Samsung motion photos are simply a complete JPEG image followed by a 16-byte marker and then a complete MP4 video. The marker itself is MotionPhoto_Data.

ExifTool Version Number         : 11.88
File Size                       : 6.9 MB
File Type                       : JPEG
File Type Extension             : jpg
MIME Type                       : image/jpeg
Make                            : samsung
Camera Model Name               : SM-G973F
[...]
Micro Video                     : 1
Micro Video Version             : 1
Micro Video Offset              : 4535831
Micro Video Presentation Timestamp Us: -1
Image Width                     : 4032
Image Height                    : 3024
Encoding Process                : Baseline DCT, Huffman coding
Bits Per Sample                 : 8
Color Components                : 3
Embedded Video Type             : MotionPhoto_Data
Embedded Video File             : (Binary data 4535775 bytes, use -b option to extract)
Aperture                        : 2.4
Image Size                      : 4032x3024
Megapixels                      : 12.2
Light Value                     : 13.9

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