Fix oob fuzz test failure

[xnorpx]

One could fix and rewrite this in many ways, but to keep small changes this is my proposal.

[xnorpx]

Fix for #586

[algesten]

This looks good to me. I wonder if @davibe or @k0nserv agree?

[davibe]

to minimize changes this could be let Some(b0) = packet.get(curr_offset) else { continue; }