Fix startup when there's no live layers in reds

src/gisaf/registry.py

@@ -623,7 +623,10 @@ class ModelRegistry:
                          inplace=True)
         df_live = pd.DataFrame.from_dict(self.geom_live_defs.values(),
                                          orient='columns'
-                                         ).set_index('store')
+                                         )
+        if len(df_live) == 0:
+            return
+        df_live.set_index('store', inplace=True)
         ## Adjust column names
         ## and add columns, to make sure pandas dtypes are not changed when the
         ## dataframes are concat