git-blame: prevent argument parsing segfault

Description:
k@samael /localhome/k/git.git/git/gitweb % git-blame --incremental
zsh: segmentation fault git blame --incremental

The 3rd branch in builtin-blame.c should also check for lacking arguments. Running that in top dir avoids the problem because the 'prefix' is NULL. The --incremental is no to blame here, it only triggers the segfault and even without that flag it goes checking argv too far.

I didn't check the pu branch, and I'm sorry if this is a dupe.

cheers,
Tommi "Kynde" Kyntola

index 7a5665f..6d51b1f 100644
@@ -2211,6 +2211,8 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
                }
                else {
                        /* (3) */
+                       if (argc <= i)
+                               usage(blame_usage);
                        path = add_prefix(prefix, argv[i]);
                        if (i + 1 == argc - 1) {
                                final_commit_name = argv[i + 1];

Thanks. Sign-off?