Adjust relationship graph to avoid nodes overlap

When the labels include the issue's Summary, they become much bigger
causing the graph's nodes to overlap.

Tweaking the graph's attributes avoids this, at the expense of a
slightly larger image.

Fixes #17594

core/relationship_graph_api.php

@@ -158,7 +158,10 @@ function relgraph_generate_rel_graph( $p_bug_id, $p_show_summary = false ) {
 	$t_view_on_click = config_get( 'relationship_graph_view_on_click' );
 	$t_neato_tool = config_get_global( 'neato_tool' );
 
-	$t_graph_attributes = array();
+	$t_graph_attributes = array(
+		'overlap'	=> 'false',
+		'overlap_scaling' => '0',
+	);
 
 	if( !empty( $t_graph_fontpath ) ) {
 		$t_graph_attributes['fontpath'] = $t_graph_fontpath;