scripts: plot.py/plotmpl.py: Stop dropping unlabeled datasets

That was confusing.

The -L/--label flag is already tricky enough to get right. Allowing
-L/--label to filter datasets is counter-intuitive and just makes it
harder to debug things.

scripts/plotmpl.py

@@ -283,12 +283,16 @@ def fold(results, by=None, x=None, y=None, defines=[], labels=None):
                     key_ += (y_,)
                 datasets[key_] = dataset
 
-    # filter/order by labels
+    # order by labels
     if labels:
         datasets_ = co.OrderedDict()
         for _, key in labels:
             if key in datasets:
                 datasets_[key] = datasets[key]
+        # include unlabeled data to help with debugging
+        for key, dataset in datasets.items():
+            if key not in datasets_:
+                datasets_[key] = datasets[key]
         datasets = datasets_
 
     return datasets
@@ -947,7 +951,7 @@ def main(csv_paths, output, *,
     for name in datasets_.keys():
         name_ = ','.join(name)
         if name_ in legend:
-            if all_labels:
+            if all_labels and name in all_labels_:
                 if all_labels_[name]:
                     legend_.append((all_labels_[name], legend[name_]))
             else: