avoid stack-smash when processing unusual commit

[Jason A. Donenfeld]

Hi Jim,

Thanks a lot for resending this. This is, indeed, a critical bug. I've
applied your patch here:
http://git.zx2c4.com/cgit/commit/?id=7757d1b046ecb67b830151d20715c658867df1ec

It would be good to tag and release a new cgit version for this
critical patch, but I don't want to trounce all over Lars' baby too
soon. After things have settled a bit, I'll consider doing that.

Thanks again for reporting this.

Jason