Naive struct check bug back in HEAD

Line 269 of scripts/base/protocols/http/main.bro seems to have
reverted back to the segfault-able version in git.

I'm also seeing this cause worker crashes:

1317736351.925801 internal error in
/usr/local/bro-870bdf796d8ae1428389ed0f3302c8a818b7e78a/share/bro/policy/protocols/ssl/cert-hash.bro,
line 20: field value missing (SSL::c$ssl)
/usr/local/bro-870bdf796d8ae1428389ed0f3302c8a818b7e78a/share/broctl/scripts/run-bro:
line 60: 16497 Aborted (core dumped) nohup $mybro $@