generic_isp: fix: Display nothing instead of 'None' for fields not filled

Signed-off-by: CapsLock <faimaison@legeox.net>

coin/billing/templates/billing/invoice_pdf.html

@@ -92,8 +92,10 @@
                 {% with member=invoice.member %}
                     {{ member.last_name }} {{ member.first_name }}<br />
                     {% if member.organization_name != "" %}{{ member.organization_name }}<br />{% endif %}
-                    {{ member.address }}<br />
-                    {{ member.postal_code }} {{ member.city}}
+                    {% if member.address %}{{member.address}}<br />{% endif %}
+                    {% if member.postal_code and member.city %}
+                        {{ member.postal_code }} {{ member.city }}
+                    {% endif %}
                 {% endwith %}
 			</td>
 		</tr>