issue with applying a unified patch of zero line context concerning the first line of a file

Hi,

I get an unexpected result when applying a unified patch of zero line
context concerning the first line of a file.
Here is the way I reproduce it:

$ echo -e "B\nC\n" >file.a
$ echo -e "A\nB\nC\n" >file.b
$ diff --unified=0 file.a file.b >file.patch
$ patch --unified file.a file.patch
patching file `file.a'
Patch attempted to create file `file.a', which already exists.
Hunk #1 FAILED at 1.
1 out of 1 hunk FAILED -- saving rejects to file.a.rej


However, if I change the number of context lines to 1, I get no error.

Here is the versions I use:

$ diff --version
diff - GNU diffutils version 2.7

$ patch --version
patch 2.5
Copyright 1988 Larry Wall
Copyright 1997 Free Software Foundation, Inc.
[...]


--
Guillaume Oriol