Graph links do not contain URL path causing links to fail

[YongBoLiu]

Describe the bug
A clear and concise description of what the bug is.
There are two relative href calls in graph.php as below, this makes graph.php does not work when called from plugins.
$.get('graph.php?action=xxxxxxxxxx');

The error is 404, NOT Found. The apache log is below.
[Mon May 20 15:37:43.709666 2019] [:error] [pid 16192] [client 9.119.131.226:39128] script '/var/www/html/cacti/plugins/gridblstat/graph.php' not found or unable to stat.

To Reproduce
Steps to reproduce the behavior:

1. Call html_graph_area() in a plugin, such as gridbstat
2. Click on the graph icon beside the graph, this will navigate to graph.php from the plugin.
3. It shows, 'Error: 404 NOT FOUND', the request URL was not found.

Expected behavior
A clear and concise description of what you expected to happen.

Change the relative href to absolute href as we did in other lines in the file graph.php.
This will make the graph.php more stronger and it will works well when call from plugins.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.

diff -u -N rtm/cacti/graph.php rtm/cacti/graph.php
--- rtm/cacti/graph.php	2019-02-28 10:52:54.000000322 +0800
+++ rtm/cacti/graph.php	2019-05-20 15:42:48.000000377 +0800
@@ -224,7 +224,7 @@
 			rra_id=$(this).attr('rra_id');
 			graph_start=$(this).attr('graph_start');
 			graph_end=$(this).attr('graph_end');
-			$.get('graph.php?action=zoom&header=false&local_graph_id='+graph_id+'&rra_id='+rra_id+'&graph_start='+graph_start+'&graph_end='+graph_end)
+			$.get(urlPath+'graph.php?action=zoom&header=false&local_graph_id='+graph_id+'&rra_id='+rra_id+'&graph_start='+graph_start+'&graph_end='+graph_end)
 				.done(function(data) {
 					$('#main').html(data);
 					$('#breadcrumbs').append('<li><a id="nav_util" href="#"><?php print __('Utility View');?></a></li>');
@@ -389,7 +389,7 @@
 	}
 
 	function graphProperties() {
-		$.get('graph.php?action=properties&header=false&local_graph_id='+graph_id+'&rra_id=<?php print get_request_var('rra_id');?>&view_type=<?php print get_request_var('view_type');?>&graph_start='+$('#graph_start').val()+'&graph_end='+$('#graph_end').val())
+		$.get(urlPath+'graph.php?action=properties&header=false&local_graph_id='+graph_id+'&rra_id=<?php print get_request_var('rra_id');?>&view_type=<?php print get_request_var('view_type');?>&graph_start='+$('#graph_start').val()+'&graph_end='+$('#graph_end').val())
 			.done(function(data) {
 				$('#data').html(data);
 			})