libs/web: add error message printing to nullsection template, fixes server side validation in SimpleForm instances

libs/web/luasrc/view/cbi/nullsection.htm

@@ -3,8 +3,25 @@
 		<legend><%=self.title%></legend>
 	<%- end %>
 	<div class="cbi-section-node" id="cbi-<%=self.config%>-<%=tostring(self):sub(8)%>">
+		<div>
 			<% self:render_children(1, scope or {}) %>
 		</div>
+		<% if self.error and self.error[1] then -%>
+			<div class="cbi-section-error">
+				<ul><% for _, e in ipairs(self.error[1]) do -%>
+					<li>
+						<%- if e == "invalid" then -%>
+							<%:One or more fields contain invalid values!%>
+						<%- elseif e == "missing" then -%>
+							<%:One or more required fields have no value!%>
+						<%- else -%>
+							<%=pcdata(e)%>
+						<%- end -%>
+					</li>
+				<%- end %></ul>
+			</div>
+		<%- end %>
+	</div>
 	<br />
 </fieldset>
 <%-