Fixed chart removing if empty array.

src/html/js/entries.js

@@ -430,6 +430,8 @@ drawChart = function(entries, element) {
           rendererOptions:{
         }}],
     });
+  } else {
+    window.chart = null;
   }
 };
 
@@ -461,6 +463,8 @@ drawPieChart = function(entries, element) {
           useAxesFormatters:false
         }
     });
+  } else {
+    window.pieChart = null;
   }
 };