FFmpegImage: free avpacket side data

[Kwiboo]

Description

Found this memory leak when looking at a memcheck log:

840 (240 direct, 600 indirect) bytes in 15 blocks are definitely lost in loss record 13,454 of 15,456
  at 0x4843AB8: malloc (vg_replace_malloc.c:298)
  by 0x4845A3B: realloc (vg_replace_malloc.c:785)
  by 0x5472997: av_packet_add_side_data (avpacket.c:303)
  by 0x5472A33: av_packet_new_side_data (avpacket.c:329)
  by 0x5473A1F: ff_side_data_set_encoder_stats (avpacket.c:654)
  by 0x57017DB: ff_mpv_encode_picture (mpegvideo_enc.c:1968)
  by 0x57EEEF7: avcodec_encode_video2 (utils.c:2023)
  by 0x894863: CFFmpegImage::CreateThumbnailFromSurface(unsigned char*, unsigned int, unsigned int, unsigned int, unsigned int, std::string const&, unsigned char*&, unsigned int&) (FFmpegImage.cpp:673)
  by 0xAFD8DB: CPicture::CreateThumbnailFromSurface(unsigned char const*, int, int, int, std::string const&) (Picture.cpp:88)
  by 0xAFE62F: CPicture::CacheTexture(unsigned char*, unsigned int, unsigned int, unsigned int, int, unsigned int&, unsigned int&, std::string const&, CPictureScalingAlgorithm::Algorithm) (Picture.cpp:268)
  by 0x8D036F: CDVDFileInfo::ExtractThumb(std::string const&, CTextureDetails&, CStreamDetails*, int) (DVDFileInfo.cpp:278)
  by 0x867707: CThumbExtractor::DoWork() (VideoThumbLoader.cpp:117)

av_packet_unref takes care of this and should leave m_outputBuffer alone

Motivation and Context

Fixes a memory leak in CFFmpegImage::CreateThumbnailFromSurface

How Has This Been Tested?

Running LibreELEC+Kodi on a WeTek Hub

Types of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the Code guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the CONTRIBUTING document
• I have added tests to cover my change
• All new and existing tests passed

[fritsch]

Seen it! Thx much.

jenkins build and merge