Bug: DeopleteRustGoToDefinition panicks for certain definitions

[alexluecke]

Steps to reproduce:

1. Navigate to src/libstd/net/addr.rs in core rust source
2. Find the code associated with SocketAddrV4:

pub struct SocketAddrV4 { inner: c::sockaddr_in }

3. Hover over sockaddr_in and use gd command to go to definition

An error is produced:

Error detected while processing function <SNR>48_DeopleteRustGoToDefinition:
line   16:
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:373:21^@note: run with `RUST_BACKTRACE=1` e
nvironment variable to display a backtrace.^@
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