fix normalized chart crashes when trend lines enabled but there is no insights...

fix normalized chart crashes when trend lines enabled but there is no insights data (#40624) (#40627)

Co-authored-by: Aleksandr Lesnenko <alxnddr@users.noreply.github.com>

frontend/src/metabase/visualizations/lib/trends.js

@@ -33,6 +33,9 @@ function computeExpression(node, x) {
 const msToDays = ms => ms / (24 * 60 * 60 * 1000);
 
 export function getNormalizedStackedTrendDatas(trendDatas) {
+  if (trendDatas.length === 0) {
+    return [];
+  }
   const count = trendDatas[0].length;
   const sums = _.range(count).map(i =>
     trendDatas.reduce((sum, trendData) => sum + trendData[i][1], 0),

frontend/src/metabase/visualizations/lib/trends.unit.spec.js

@@ -36,4 +36,8 @@ describe("getNormalizedStackedTrendDatas", () => {
       ]),
     ]);
   });
+
+  it("should return an empty array when there is no trend data", () => {
+    expect(getNormalizedStackedTrendDatas([])).toStrictEqual([]);
+  });
 });