Don't create cert if one exists

src/freedombone-app-jitsi

     echo '  }' >> $jitsi_nginx_site
     echo '}' >> $jitsi_nginx_site
 
-    function_check create_site_certificate
-    create_site_certificate ${JITSI_DOMAIN_NAME} 'yes'
+    if [ ! -f /etc/ssl/certs/${JITSI_DOMAIN_NAME}.pem ]; then
+        function_check create_site_certificate
+        create_site_certificate ${JITSI_DOMAIN_NAME} 'yes'
+    fi
 
     if [ -f /etc/ssl/certs/${JITSI_DOMAIN_NAME}.crt ]; then
         mv /etc/ssl/certs/${JITSI_DOMAIN_NAME}.crt /etc/ssl/certs/${JITSI_DOMAIN_NAME}.pem