Prevent empty convergence plot Error when n_iteration=1 (#2371)

* Add an argument check the convergence plot is empty or not before exporting the plot, prevent the sim fail due to plot is empty

* added my infotmation in mailmap

.mailmap

@@ -95,6 +95,8 @@ Jenny Yu <yuyizh1112@gmail.com>
 Jenny Yu <yuyizh1112@gmail.com> yuyizh <yuyizh1112@gmail.com>
 Jenny Yu <yuyizh1112@gmail.com> Jenny Yu <80535029+yuyizheng1112@users.noreply.github.com>
 
+Jing Lu <lujingeve158@gmail.com>
+
 John Reichenbach <56849859+jreichenbach-msu@users.noreply.github.com>
 
 Jordi Eguren <jordi.eguren.brown@gmail.com>

tardis/visualization/tools/convergence_plot.py

@@ -424,7 +424,7 @@ def update(self, export_convergence_plots=False, last=False):
 
         # the display function expects a Widget, while
         # fig.show() returns None, which causes the TraitError.
-        if export_convergence_plots:
+        if export_convergence_plots and (self.plasma_plot is not None):
             with suppress(TraitError):
                 display(
                     widgets.VBox(