videoio: valgrind issue on ffmpeg_16bit test (2022-12-19)

[alalek]

relates #22894

Report: http://pullrequest.opencv.org/buildbot/builders/master_valgrind-lin64-debug/builds/100002

[----------] 4 tests from videoio_ffmpeg_16bit
[ RUN      ] videoio_ffmpeg_16bit.basic/0, where GetParam() = ("FFV1", "avi", false, true)
==16868== Conditional jump or move depends on uninitialised value(s)
==16868==    at 0x8E49969: ??? (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868==    by 0x8E4E047: ??? (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868==    by 0x924DDEE: avcodec_default_execute (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868==    by 0x8E503F9: ??? (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868==    by 0x8E072B6: avcodec_encode_video2 (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868==    by 0x8E0769C: ??? (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868==    by 0x8E07849: avcodec_send_frame (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868==    by 0x50DDAA8: icv_av_write_frame_FFMPEG(AVFormatContext*, AVStream*, AVCodecContext*, unsigned char*, unsigned int, AVFrame*, int) (cap_ffmpeg_impl.hpp:2325)
==16868==    by 0x50E076F: CvVideoWriter_FFMPEG::writeFrame(unsigned char const*, int, int, int, int, int) (cap_ffmpeg_impl.hpp:2501)
==16868==    by 0x50E098C: cvWriteFrame_FFMPEG (cap_ffmpeg_impl.hpp:3263)
==16868==    by 0x50E0A88: cv::(anonymous namespace)::CvVideoWriter_FFMPEG_proxy::write(cv::_InputArray const&) (cap_ffmpeg.cpp:178)
==16868==    by 0x5080B52: cv::VideoWriter::write(cv::_InputArray const&) (cap.cpp:676)
==16868==  Uninitialised value was created by a stack allocation
==16868==    at 0x8E4967E: ??? (in /usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100)
==16868== 
{
   <insert_a_suppression_name_here>
   Memcheck:Cond
   obj:/usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100
   obj:/usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100
   fun:avcodec_default_execute
   obj:/usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100
   fun:avcodec_encode_video2
   obj:/usr/lib/x86_64-linux-gnu/libavcodec.so.57.107.100
   fun:avcodec_send_frame
   fun:_ZL25icv_av_write_frame_FFMPEGP15AVFormatContextP8AVStreamP14AVCodecContextPhjP7AVFramei
   fun:_ZN20CvVideoWriter_FFMPEG10writeFrameEPKhiiiii
   fun:cvWriteFrame_FFMPEG
   fun:_ZN2cv12_GLOBAL__N_126CvVideoWriter_FFMPEG_proxy5writeERKNS_11_InputArrayE
   fun:_ZN2cv11VideoWriter5writeERKNS_11_InputArrayE
}
[ WARN:0@230.320] global cap_ffmpeg_impl.hpp:1055 open VIDEOIO/FFMPEG: BGR conversion turned OFF, decoded frame will be returned in its original format. Multiplanar formats are not supported by the backend. Only GRAY8/GRAY16LE pixel formats have been tested. Use at your own risk.
[       OK ] videoio_ffmpeg_16bit.basic/0 (7044 ms)
[ RUN      ] videoio_ffmpeg_16bit.basic/1, where GetParam() = ("FFV1", "mkv", false, true)
==16868== 
==16868== More than 10000000 total errors detected.  I'm not reporting any more.
==16868== Final error counts will be inaccurate.  Go fix your program!
==16868== Rerun with --error-limit=no to disable this cutoff.  Note
==16868== that errors may occur in your program without prior warning from
==16868== Valgrind, because errors are no longer being displayed.
==16868==