bugfix in previously dead code

src/Dataloaders.jl

@@ -103,7 +103,7 @@ function segment(file, window, trackid, step, class)
     @assert 1 < step < length(ts)
     @inbounds anchortime = round(ts[step]; digits=4)
     segmentdata = if isnothing(window.samplerate)
-        @assert track isa LarvaBase.TimeSeries
+        @assert track isa LarvaBase.TimeSeries "Not implemented; try defining samplerate"
         t0, t1 = anchortime - window.durationbefore, anchortime + window.durationafter
         [(t, x) for (t, x) in track if t0 <= t <= t1]
     else
@@ -608,9 +608,13 @@ function sample(sampler, file, window, counts, features; verbose=false)
             end
             Formats.load!(file′)
         end
-    elseif isempty(file.timeseries)
+    else
+        isempty(file.timeseries) || empty!(file.timeseries)
+        capabilities = [cap[1] for cap in file.capabilities]
         for capability in (:spine, :outline, :tags)
-            capability in file.capabilities && capability ∉ features && Formats.drop_record!(file, capability)
+            if capability in capabilities && capability ∉ features
+                Formats.drop_record!(file, capability)
+            end
         end
     end