CloudWatch: Avoid exception while accessing results (#17283)

When accessing the `series` property of query results, if a query is
hidden, an exception is thrown. This is caused by lack of checks to
verify that the query result exists before accessing the `series`
property.

Closes #17112

public/app/plugins/datasource/cloudwatch/datasource.ts

@@ -149,12 +149,14 @@ export default class CloudWatchDatasource extends DataSourceApi<CloudWatchQuery>
       if (res.results) {
         for (const query of request.queries) {
           const queryRes = res.results[query.refId];
-          for (const series of queryRes.series) {
-            const s = { target: series.name, datapoints: series.points } as any;
-            if (queryRes.meta.unit) {
-              s.unit = queryRes.meta.unit;
+          if (queryRes) {
+            for (const series of queryRes.series) {
+              const s = { target: series.name, datapoints: series.points } as any;
+              if (queryRes.meta.unit) {
+                s.unit = queryRes.meta.unit;
+              }
+              data.push(s);
             }
-            data.push(s);
           }
         }
       }