swcale produces bright green when going from grayf32 to gbrpf32

[Leo Izen]

Summary of the bug:
Swscale produces bright green RGB data when converting from grayf32 to gbrpf32.

How to reproduce:

$ ffmpeg -i rose.pfm -vf scale,format=gbrpf32le rose2.pfm
ffmpeg version N-92323-g5230257ea1 Copyright (c) 2000-2023 the FFmpeg developers
  built with gcc 13.2.1 (GCC) 20230801
  configuration: --prefix=/home/leo/.local --enable-gpl --enable-version3 --enable-nonfree --enable-shared --disable-static --disable-htmlpages --enable-manpages --disable-podpages --disable-txtpages --enable-frei0r --enable-gcrypt --enable-gmp --enable-gnutls --enable-lcms2 --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcelt --enable-libcdio --enable-libdav1d --enable-libdc1394 --enable-libfdk-aac --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libiec61883 --enable-libjack --enable-libjxl --enable-libkvazaar --enable-libmodplug --enable-libmp3lame --enable-libopus --enable-libplacebo --enable-libpulse --enable-librav1e --enable-librsvg --enable-librtmp --enable-librubberband --enable-libsmbclient --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libsvtav1 --enable-libtesseract --enable-libtheora --enable-libtwolame --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpl --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxcb-shm --enable-libxcb-xfixes --enable-libxcb-shape --enable-libxvid --enable-libzimg --enable-libzmq --enable-openal --enable-opengl --disable-openssl --enable-pic --enable-ffnvcodec --enable-libdrm --enable-vapoursynth --enable-vulkan --extra-cflags='-Wno-format-truncation -Wno-stringop-overflow -Wno-array-bounds'
  libavutil      58. 32.100 / 58. 32.100
  libavcodec     60. 35.100 / 60. 35.100
  libavformat    60. 18.100 / 60. 18.100
  libavdevice    60.  4.100 / 60.  4.100
  libavfilter     9. 14.100 /  9. 14.100
  libswscale      7.  6.100 /  7.  6.100
  libswresample   4. 13.100 /  4. 13.100
  libpostproc    57.  4.100 / 57.  4.100
Input #0, pfm_pipe, from 'rose.pfm':
  Duration: N/A, bitrate: N/A
  Stream #0:0: Video: pfm, grayf32le, 70x46, 25 fps, 25 tbr, 25 tbn
File 'rose2.pfm' already exists. Overwrite? [y/N] y
Stream mapping:
  Stream #0:0 -> #0:0 (pfm (native) -> pfm (native))
Press [q] to stop, [?] for help
Output #0, image2, to 'rose2.pfm':
  Metadata:
    encoder         : Lavf60.18.100
  Stream #0:0: Video: pfm, gbrpf32le(pc, gbr/unknown/unknown, progressive), 70x46, q=2-31, 200 kb/s, 25 fps, 25 tbn
    Metadata:
      encoder         : Lavc60.35.100 pfm
[image2 @ 0x55f568894100] The specified filename 'rose2.pfm' does not contain an image sequence pattern or a pattern is invalid.
[image2 @ 0x55f568894100] Use a pattern such as %03d for an image sequence or use the -update option (with -frames:v 1 if needed) to write a single image.
[out#0/image2 @ 0x55f568893340] video:38kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown
frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.00 bitrate=N/A speed=   0x    

Samples attached.