Using threads while looping on events

This issue has been copied from https://github.com/KM3NeT/KM3io.jl/issues/1 (originally created by @guirriec)

Running this with --threads=2 is failing

using KM3io, KM3NeTTestData

f = ROOTFile(datapath("offline", "numucc.root"))

Threads.@threads for ev in f.offline
#for ev in f.offline
@show ev
end

It is running fine without threads (comment out for loop)