Sometimes get file rename error at end of download

[Nick Payne]

Running get_iplayer 3.06 on Win10 x64. Sometimes the rename of the mp4
file at the end of a download fails. ffmpeg creates the partial.mp4 file
without any problem, but get_iplayer.pl then fails to rename
.partial.mp4 to mp4. It's not a permissions problem, else ffmpeg would
not be able to create the partial.mp4 file.

The problem doesn't happen on every download, maybe one in three. All
downloads go into the same folder, in which I have full permissions.
Relevant part of the console output from running with --verbose.

INFO: Converting to MP4
INFO: Command: "ffmpeg" "-loglevel" "fatal" "-stats" "-y" "-i"
"D:\Users\Nick\Videos\iplayer\Peaky_Blinders-s04e02-Heathens.dash.m4a"
"-i"
"D:\Users\Nick\Videos\iplayer\Peaky_Blinders-s04e02-Heathens.dash.m4v"
"-c:v" "copy" "-c:a" "copy" "-map" "0:a:0" "-map" "1:v:0"
"D:\Users\Nick\Videos\iplayer\Peaky_Blinders-s04e02-Heathens.partial.mp4"
frame=173860 fps=20666 q=-1.0 Lsize= 1853690kB time=00:57:57.16
bitrate=4367.2kbits/s speed= 413x
INFO: Command exit code 0 (raw code = 0)
ERROR: Could not rename file:
D:\Users\Nick\Videos\iplayer\Peaky_Blinders-s04e02-Heathens.partial.mp4
ERROR: Destination file name:
D:\Users\Nick\Videos\iplayer\Peaky_Blinders-s04e02-Heathens.mp4
INFO: Skipping all versions of this programme
ERROR: Failed tv: 'Peaky Blinders: Series 4 - 2. Heathens (b09gvn5j)'