Fix dangling pointer in format_email.

[ehuss]

The code was creating an Oid object, taking a pointer to it, and then immediately dropping it. The fix is to use a local variable to hold the value.

Fixes #613

[joshtriplett]

@ehuss Thanks for the fix! The same issue would apply to commit.author().raw() a few lines later, right?

[ehuss]

The same issue would apply to commit.author().raw() a few lines later, right?

I don't think so. The Signature returned from commit.author() is not owned (see from_raw_const). Thus when the Signature is dropped, the raw pointer is still alive.

[joshtriplett]

You're right. I was trying to see if there were other instances of this pattern in the codebase, and searched for ().raw in the process.

I wonder if there's some reasonable way we could get the compiler to identify issues like this, even though they use raw pointers.