Writes to RollingFileWriter don't return bytes written causing Julia error

[krynju]

here https://github.com/JuliaLang/julia/blame/e4ee485e90961018b7e53ce14b8b99335953e176/base/io.jl#L755

┌ Warning: Process I/O error
│   exception =
│    MethodError: no method matching +(::Int64, ::Nothing)
│
│    Closest candidates are:
│      +(::Any, ::Any, !Matched::Any, !Matched::Any...)
│       @ Base operators.jl:578
│      +(::T, !Matched::T) where T<:Union{Int128, Int16, Int32, Int64, Int8, UInt128, UInt16, UInt32, UInt64, UInt8}
│       @ Base int.jl:87
│      +(::Union{Int16, Int32, Int64, Int8}, !Matched::BigInt)
│       @ Base gmp.jl:545
│      ...
│
│    Stacktrace:
│     [1] write
│       @ ./io.jl:755 [inlined]
│     [2] macro expansion
│       @ ./process.jl:300 [inlined]
│     [3] (::Base.var"#764#765"{RollingFileWriter, Bool, Base.PipeEndpoint, RollingFileWriter, Base.PipeEndpoint})()
│       @ Base ./task.jl:514
└ @ Base process.jl:302