browser: cleanup datasets panel for empty h5 files

this fix makes sure the datasets panel is cleared if an h5 file is empty or the datasets and archive groups are empty

artiq/browser/files.py

@@ -197,8 +197,9 @@ class FilesDock(QtWidgets.QDockWidget):
                         logger.warning("dataset '%s' is both in archive and "
                                        "outputs", k)
                     rd[k] = (True, v[()])
-            if rd:
+
             self.datasets.init(rd)
+
         self.dataset_changed.emit(info.filePath())
 
     def list_activated(self, idx):