[BUG?] git range-diff -Ix @{1}... segfaults

[Junio C Hamano <gitster@xxxxxxxxx>]

It does not seem to trigger with an empty range, e.g.

    $ git range-diff -Ix HEAD...
    $ git range-diff -Ix HEAD~...
    -:  ---------- > 1:  0a0bc7d03a scalar: accept -C and -c opt...

but when it needs real comparison, the -I seems to kill the command
quite easily.

THanks.