luci-app-statistics: render all graphs on refresh if no summary

Previously, if there would usually be a summary page for the data
but this was not happening because there was only a single instance
(e.g. a single wifi interface), the refresh would mistakenly
request the summary rather than the existing data.

i.e. graphs would mysteriously disappear on refresh.

Signed-off-by: James Haggerty <james.haggerty@morsemicro.com>

applications/luci-app-statistics/htdocs/luci-static/resources/view/statistics/graphs.js

@@ -74,6 +74,7 @@ return view.extend({
 					'data-tab-title': multiple ? title : null,
 					'data-plugin': plugin,
 					'data-plugin-instance': plugin_instance,
+					'data-is-index': i || render_instances.length == 1 ? null : true,
 					'data-is-index': i ? null : true,
 					'cbi-tab-active': function(ev) { activeInstance = ev.target.getAttribute('data-plugin-instance') }
 				}, blobs.map(function(blob) {