Fixed application of function to self in LabelledData.map method

The old code would lose the application of the map function to self for
deep indexable objects. This fix now means that id values are properly
propagated via the map method.

holoviews/core/dimension.py

@@ -329,14 +329,15 @@ def map(self, map_fn, specs=None, clone=True):
         specification applies.
         """
         applies = specs is None or any(self.matches(spec) for spec in specs)
-        mapped = map_fn(self) if applies else self
+
         if self._deep_indexable:
-            deep_mapped = mapped.clone(shared_data=False) if clone else mapped
-            for k, v in mapped.items():
+            deep_mapped = self.clone(shared_data=False) if clone else self
+            for k, v in self.items():
                 deep_mapped[k] = v.map(map_fn, specs, clone)
+            if applies: deep_mapped = map_fn(deep_mapped)
             return deep_mapped
         else:
-            return mapped
+            return map_fn(self) if applies else self
 
 
     def __getstate__(self):