Fix of about page crash if no president or CGU file

re2o/templates/re2o/about.html

@@ -43,8 +43,10 @@ with this program; if not, write to the Free Software Foundation, Inc.,
     <h4>{% trans "Publication manager" %}</h4>
     <p>{{ president }} - {% trans "President of " %} {{ option.pseudo }}</p>
 
+    {% if gtu %}
     <h4>{% trans "General Terms of Use" %}</h4>
     <p><a href='{{ gtu.url }}' download='CGU'>{{ gtu }}</a></p>
+    {% endif %}
 
     {% if option.description %}
     <h4>{% trans "Additional information" %}</h4>

re2o/views.py

@@ -115,13 +115,18 @@ def about_page(request):
 
     dependencies = settings.INSTALLED_APPS + settings.MIDDLEWARE_CLASSES
 
+    try:
+        president = Mandate.get_mandate().president.get_full_name()
+    except:
+        president = _("Unable to get the information.")
+
     return render(
         request,
         "re2o/about.html",
         {
             "option": option,
             "gtu": general.GTU,
-            "president": Mandate.get_mandate().president.get_full_name(),
+            "president": president,
             "git_info_contributors": git_info_contributors,
             "git_info_remote": git_info_remote,
             "git_info_branch": git_info_branch,