JuliaSyntax parser errors: `BoundsError: attempt to access empty SubString{String} at index [0]`

[pchintalapudi]

Failure occurs while generating docs in JuliaLang/julia#50319.

Seen here: https://buildkite.com/julialang/julia-master/builds/25340#0189007d-d1fa-43ba-a9f6-7037bbf16149

[c42f]

This is fixed in the latest dev branch.