Fixed an error, where we checked for an empty condition table (which is true if we only have an index) (#237)

Author: PaulJonasJost

src/petab_gui/views/simple_plot_view.py

@@ -180,7 +180,7 @@ def _render_on_main_thread(self, payload):
             meas_df is None
             or meas_df.empty
             or cond_df is None
-            or cond_df.empty
+            or not len(cond_df) > 0
         ):
             self._update_tabs(None)
             return