rustdoc ICE (3/3) in markdown - unwrap on nil value

[Mark-Simulacrum]

Possibly fixed by #60802 (awaiting beta backport approval)

root: shellwords - 1 detected crates which regressed due to this; cc @jimmycuadra

 * shellwords-1.0.0: [start](https://crater-reports.s3.amazonaws.com/beta-1.36-2/1.35.0/reg/shellwords-1.0.0/log.txt) v. [end](https://crater-reports.s3.amazonaws.com/beta-1.36-2/beta-2019-05-30/reg/shellwords-1.0.0/log.txt); cc @jimmycuadra

[QuietMisdreavus]

Confirming the ICE is no longer present on nightly.

[jonas-schievink]

Closing this as fixed.