Conditional jump or move depends on uninitialised value with small input

[Clément Bœsch]

☭ valgrind ./ffmpeg_g -f lavfi -i color=white:s=2x2,format=rgba,scale=10x10 -frames:v 1 -f null -
==95117== Memcheck, a memory error detector
==95117== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==95117== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==95117== Command: ./ffmpeg_g -f lavfi -i color=white:s=2x2,format=rgba,scale=10x10 -frames:v 1 -f null -
==95117==
ffmpeg version N-96482-ge931119a41 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 9.2.0 (GCC)
  configuration: --cc=/usr/bin/gcc
  libavutil      56. 38.100 / 56. 38.100
  libavcodec     58. 66.100 / 58. 66.100
  libavformat    58. 35.104 / 58. 35.104
  libavdevice    58.  9.103 / 58.  9.103
  libavfilter     7. 71.100 /  7. 71.100
  libswscale      5.  6.100 /  5.  6.100
  libswresample   3.  6.100 /  3.  6.100
==95117== Conditional jump or move depends on uninitialised value(s)
==95117==    at 0xF25462: yuv2rgb_full_1_c_template (output.c:2102)
==95117==    by 0xF25462: yuv2rgba32_full_1_c (output.c:2142)
==95117==    by 0xF05B31: packed_vscale (vscale.c:134)
==95117==    by 0xF01D20: swscale (swscale.c:503)
==95117==    by 0xF02D5C: sws_scale (swscale.c:978)
==95117==    by 0x3A5496: scale_slice.isra.0 (vf_scale.c:647)
==95117==    by 0x3A5C76: scale_frame (vf_scale.c:809)
==95117==    by 0x3A5D77: filter_frame (vf_scale.c:823)
==95117==    by 0x2C85FC: ff_filter_frame_framed (avfilter.c:1066)
==95117==    by 0x2C85FC: ff_filter_frame_to_filter (avfilter.c:1214)
==95117==    by 0x2C85FC: ff_filter_activate_default (avfilter.c:1263)
==95117==    by 0x2C85FC: ff_filter_activate (avfilter.c:1425)
==95117==    by 0x2CBC1C: get_frame_internal (buffersink.c:108)
==95117==    by 0x2A6917: lavfi_read_packet (lavfi.c:412)
==95117==    by 0x5AEB2E: ff_read_packet (utils.c:857)
==95117==    by 0x5AF4AA: read_frame_internal (utils.c:1588)
==95117==
Input #0, lavfi, from 'color=white:s=2x2,format=rgba,scale=10x10':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: rawvideo (RGBA / 0x41424752), rgba, 10x10 [SAR 1:1 DAR 1:1], 25 tbr, 25 tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> wrapped_avframe (native))
Press [q] to stop, [?] for help
Output #0, null, to 'pipe:':
  Metadata:
    encoder         : Lavf58.35.104
    Stream #0:0: Video: wrapped_avframe, rgba, 10x10 [SAR 1:1 DAR 1:1], q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc
    Metadata:
      encoder         : Lavc58.66.100 wrapped_avframe
frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A speed=0.113x
video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
==95117==
==95117== HEAP SUMMARY:
==95117==     in use at exit: 0 bytes in 0 blocks
==95117==   total heap usage: 2,725 allocs, 2,725 frees, 926,979 bytes allocated
==95117==
==95117== All heap blocks were freed -- no leaks are possible
==95117==
==95117== Use --track-origins=yes to see where uninitialised values come from
==95117== For lists of detected and suppressed errors, rerun with: -s
==95117== ERROR SUMMARY: 100 errors from 1 contexts (suppressed: 0 from 0)