Fix bug in recent part scheduling table (#3566)

* Gotta make a variable to reference a variable

* Fix scaling issues

* Hey, it's only a suggestion

* Fix quantity display in build order table

* Logic fix for destroying / refreshing chart

* Better handling of edge cases

* Fix issue with "undefined" labels

* Speculative should be a question mark

InvenTree/part/templates/part/detail.html

@@ -435,8 +435,12 @@
         var chart = loadPartSchedulingChart('part-schedule-chart', {{ part.pk }});
 
         $('#btn-schedule-reload').click(function() {
-            chart.destroy();
-            loadPartSchedulingChart('part-schedule-chart', {{ part.pk }});
+
+            if (chart != null) {
+                chart.destroy();
+            }
+
+            chart = loadPartSchedulingChart('part-schedule-chart', {{ part.pk }});
         });
     });