[PATCH] cmd: Fix copying when the dest is one of the sources.

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=26929

Your paranoid android.


=== wvistau64 (32 bit) ===
batch.c:313: Test failed: unexpected char 0x27 position 0 in line 456 (got ''--a--c---'', wanted ''--a------'@or_broken@'--a--------'@or_broken@'%~ai'')

=== wvistau64 (64 bit) ===
batch.c:313: Test failed: unexpected char 0x27 position 0 in line 456 (got ''--a--c---'', wanted ''--a------'@or_broken@'--a--------'@or_broken@'%~ai'')