git add -p: demonstrate failure when staging both mode and hunk

git add -p: demonstrate failure when staging both mode and hunk

When trying to stage changes to file which has also pending `chmod +x`,
`git add -p` produces lots of 'Use of uninitialized value ...' warnings
and fails to do the job:

    $ echo content >> file
    $ chmod +x file
    $ git add -p
    diff --git a/file b/file
    index e69de29..d95f3ad
    --- a/file
    +++ b/file
    old mode 100644
    new mode 100755
    Stage mode change [y,n,q,a,d,/,j,J,g,?]? y
    @@ -0,0 +1 @@
    +content
    Stage this hunk [y,n,q,a,d,/,K,g,e,?]? y
    Use of uninitialized value $o_ofs in addition (+) at .../git-add--interactive line 776.
    Use of uninitialized value $ofs in numeric le (<=) at .../git-add--interactive line 806.
    Use of uninitialized value $o0_ofs in concatenation (.) or string at .../git-add--interactive line 830.
    Use of uninitialized value $n0_ofs in concatenation (.) or string at .../git-add--interactive line 830.
    Use of uninitialized value $o_ofs in addition (+) at .../git-add--interactive line 776.
    fatal: corrupt patch at line 5
    diff --git a/file b/file
    index e69de29..d95f3ad
    --- a/file
    +++ b/file
    @@ -,0 + @@
    +content

Signed-off-by: Kirill Smelkov <kirr@mns.spb.ru>
Signed-off-by: Junio C Hamano <gitster@pobox.com>