Tokenization error with nested multiline comments

[c42f]

As reported at JuliaLang/Tokenize.jl#205

julia> collect(tokenize("#=#==#=#"))
2-element Vector{Tokenize.Tokens.Token}:
 1,1-1,8          ERROR          "#=#==#=#"
 1,9-1,8          ENDMARKER      ""

julia> collect(JuliaSyntax.Tokenize.tokenize("#=#==#=#"))
2-element Vector{JuliaSyntax.Tokenize.Token}:
 0-7        ErrorEofMultiComment
 8-7        EndMarker