[Regression] `import` is broken for non-label files

larvatagger.jl import table.csv --framerate=30

triggers

ERROR: LoadError: AssertionError: labels isa Vector{String} || labels isa Vector{Symbol}
Stacktrace:
 [1] getprimarylabels(attributes::OrderedDict{Symbol, Any}, attrname::Tuple{Tuple{Symbol, Symbol}, Symbol})
   @ PlanarLarvae.Datasets ~/.julia/packages/PlanarLarvae/QEjfc/src/Datasets.jl:770
 [2] getlabels(dataset::Run; labels::Nothing, attrname::Tuple{Tuple{Symbol, Symbol}, Symbol}, store::Bool)
   @ PlanarLarvae.Datasets ~/.julia/packages/PlanarLarvae/QEjfc/src/Datasets.jl:826
 [3] encodelabels!(run::Run; labels::Nothing, attrname::Tuple{Tuple{Symbol, Symbol}, Symbol}, storelabels::Bool)
   @ PlanarLarvae.Datasets ~/.julia/packages/PlanarLarvae/QEjfc/src/Datasets.jl:880
 [4] encodelabels!
   @ ~/.julia/packages/PlanarLarvae/QEjfc/src/Datasets.jl:878 [inlined]
 [5] main(args::Vector{String}; exit_on_error::Bool)
   @ Main .../src/cli.jl:159
 [6] main (repeats 2 times)
   @ .../src/cli.jl:86 [inlined]
 [7] top-level scope
   @ .../scripts/larvatagger.jl:21