segfault for git log --graph --no-walk --grep a

Hallo,

I just found that git crashes with a segmentation fault when calling $ git log --graph --no-walk --grep pattern

It happens both for version 1.7.10.4 from Debian (wheezy,amd64) and a fresh compiled git from github (git.git repository, master).

For the error to occure, the pattern must match the commit message in HEAD.

How to reproduce:
  git init .
  git commit -m 'text1' --allow-empty
  git commit -m 'text2' --allow-empty
  git log --graph --no-walk --grep 'text2'

And here is coredump I got:

Core was generated by `git log --graph --no-walk --grep text2'. Program terminated with signal 11, Segmentation fault. #0 __strlen_sse42 () at ../sysdeps/x86_64/multiarch/strlen-sse4.S:32 #1 0x00000000004cc13e in commit_match (opt=0x7fffbd0ee500, commit=0x216d1a8) at revision.c:2306 #2 get_commit_action (revs=0x7fffbd0ee500, commit=0x216d1a8) at revision.c:2338 #3 0x00000000004984b4 in graph_is_interesting (commit=<optimized out>, graph=<error reading variable: Unhandled dwarf expression opcode 0xfa>) at graph.c:330 #4 0x0000000000498569 in first_interesting_parent (graph=graph@entry=0x21629c0) at graph.c:369 #5 0x000000000049965e in graph_update (graph=0x21629c0, commit=<optimized out>) at graph.c:593 #6 0x00000000004cc7a9 in get_revision (revs=revs@entry=0x7fffbd0ee500) at revision.c:2580 #7 0x000000000043988a in cmd_log_walk (rev=rev@entry=0x7fffbd0ee500) at builtin/log.c:309 #8 0x000000000043a398 in cmd_log (argc=9, argv=0x2162930, prefix=0x0) at builtin/log.c:582 #9 0x0000000000405988 in run_builtin (argv=0x2162930, argc=9, p=0x751438) at git.c:281 #10 handle_internal_command (argc=9, argv=0x2162930) at git.c:443 #11 0x0000000000404df2 in run_argv (argv=0x7fffbd0eec00, argcp=0x7fffbd0eec0c) at git.c:489 #12 main (argc=9, argv=0x2162930) at git.c:564

it happens in file revision.c:2306 because "commit->buffer" is zero:

                retval = grep_buffer(&opt->grep_filter,
                                     commit->buffer, strlen(commit->buffer));

thank you all, for this awesome software. Thomas