tests/test-symlinks.out

Prevent type exception on concatenation if diffstat returns None.

This will most often occur if diffstat is not installed in the
target platform, though may also happen in other cases where
diffstat fails to execute.

Signed-off-by: Sean Dague <[e-mail]>

adding foo
adding bomb
adding a.c
adding dir/a.o
adding dir/b.o
! a.c
! dir/a.o
! dir/b.o
? .hgignore
a.c: unsupported file type (type is fifo)
! a.c
# test absolute path through symlink outside repo
A f
# try symlink outside repo to file inside
abort: ../z not under root