revert to previous behavior for displaying stopped containers

* Previously, a stopped container was completely removed from the chart/tooltip during the time period when it was not running. In the last few releases, the container remained in the chart with zero values if it was running at any time during the chart's duration. This restores the previous functionality.

beszel/site/src/components/charts/container-chart.tsx

@@ -116,9 +116,9 @@ export default memo(function ContainerChart({
 		}
 		// data function
 		if (isNetChart) {
-			obj.dataFunction = (key: string, data: any) => (data[key]?.nr ?? 0) + (data[key]?.ns ?? 0)
+			obj.dataFunction = (key: string, data: any) => (data[key]?.nr ?? null) + (data[key]?.ns ?? null)
 		} else {
-			obj.dataFunction = (key: string, data: any) => data[key]?.[dataKey] ?? 0
+			obj.dataFunction = (key: string, data: any) => data[key]?.[dataKey] ?? null
 		}
 		return obj
 	}, [])