fix(graph-panel): fixes broken PNG rendering

When refactoring y-axies for graph panel these
was forgotten and which caused the graphite datasource
to send invalid data.

closes #5025

public/app/plugins/panel/graph/graph.js

@@ -452,12 +452,21 @@ function (angular, $, moment, _, kbn, GraphTooltip) {
           url += panel.fill !== 0 ? ('&areaAlpha=' + (panel.fill/10).toFixed(1)) : '';
           url += panel.linewidth !== 0 ? '&lineWidth=' + panel.linewidth : '';
           url += panel.legend.show ? '&hideLegend=false' : '&hideLegend=true';
-          url += panel.grid.leftMin !== null ? '&yMin=' + panel.grid.leftMin : '';
-          url += panel.grid.leftMax !== null ? '&yMax=' + panel.grid.leftMax : '';
-          url += panel.grid.rightMin !== null ? '&yMin=' + panel.grid.rightMin : '';
-          url += panel.grid.rightMax !== null ? '&yMax=' + panel.grid.rightMax : '';
-          url += panel['x-axis'] ? '' : '&hideAxes=true';
-          url += panel['y-axis'] ? '' : '&hideYAxis=true';
+
+          if (panel.yaxes && panel.yaxes.length > 0) {
+            var showYaxis = false;
+            for(var i = 0; panel.yaxes.length > i; i++) {
+              if (panel.yaxes[i].show) {
+                url += (panel.yaxes[i].min !== null && panel.yaxes[i].min !== undefined) ? '&yMin=' + panel.yaxes[i].min : '';
+                url += (panel.yaxes[i].max !== null && panel.yaxes[i].max !== undefined) ? '&yMax=' + panel.yaxes[i].max : '';
+                showYaxis = true;
+                break;
+              }
+            }
+            url += showYaxis ? '' : '&hideYAxis=true';
+          }
+
+          url += panel.xaxis.show ? '' : '&hideAxes=true';
 
           switch(panel.yaxes[0].format) {
             case 'bytes':