Only list guardians with phone numbers in printed list.

ticdesk_org/templates/ticdesk_org/list_participants.tex

@@ -25,8 +25,10 @@
   \begin{flushleft}
    \nohyphens{{ person.mobile|embrace }} \newline ~%
    {% for guardian in person.guardians_parents %}%
-    \newline
-    \nohyphens{{ guardian.cn|embrace }}: \nohyphens{{ guardian.mobile|embrace }}%
+    {% if guardian.mobile %}%
+     \newline
+     \nohyphens{{ guardian.cn|embrace }}: \nohyphens{{ guardian.mobile|embrace }}%
+    {% endif %}%
    {% endfor %}
   \end{flushleft}
  } &