LJpegDecompressor predictor mode 7 support

[LebedevRI]

Comes up in iPhone 12 Pro raws: https://raw.pixls.us/getfile.php/4264/raw/IMG_1361.DNG

/tmp/IMG_1361.DNG                                      : starting decoding ... 
/tmp/IMG_1361.DNG failed: ../src/librawspeed/decompressors/AbstractDngDecompressor.cpp:218: void rawspeed::AbstractDngDecompressor::decompress() const: Too many errors encountered. Giving up. First Error:
../src/librawspeed/decompressors/LJpegDecompressor.cpp:91: virtual void rawspeed::LJpegDecompressor::decodeScan(): Unsupported predictor mode: 7
Total decoding time: 0s

WARNING: the following 1 tests have failed:
/tmp/IMG_1361.DNG failed: ../src/librawspeed/decompressors/AbstractDngDecompressor.cpp:218: void rawspeed::AbstractDngDecompressor::decompress() const: Too many errors encountered. Giving up. First Error:
../src/librawspeed/decompressors/LJpegDecompressor.cpp:91: virtual void rawspeed::LJpegDecompressor::decodeScan(): Unsupported predictor mode: 7
==46741==LeakSanitizer has encountered a fatal error.
==46741==HINT: For debugging, try setting environment variable LSAN_OPTIONS=verbosity=1:log_threads=1
==46741==HINT: LeakSanitizer does not work under ptrace (strace, gdb, etc)