Parsers reads out of bounds in checkdelim!

[KristofferC]

❯ julia --check-bounds=yes --compiled-modules=no
julia> using Parsers

julia> Parsers.checkdelim!(codeunits("::::"), 1, 4, Parsers.Options(delim = "::", ignorerepeated = true)) == 5
ERROR: BoundsError: attempt to access 4-codeunit String at index [5]
Stacktrace:
 [1] checkbounds
   @ ./strings/basic.jl:216 [inlined]
 [2] codeunit
   @ ./strings/string.jl:117 [inlined]
 [3] getindex
   @ ./strings/basic.jl:756 [inlined]
 [4] peekbyte
   @ ~/.julia/packages/Parsers/gi2J3/src/utils.jl:345 [inlined]
 [5] checkdelim!(source::Base.CodeUnits{UInt8, String}, pos::Int64, len::Int64, options::Parsers.Options)
   @ Parsers ~/.julia/packages/Parsers/gi2J3/src/Parsers.jl:375
 [6] top-level scope
   @ REPL[2]:1

(running with --compiled-modules=no to make sure no precompile file with bounds checking turned off is cached)