Length check against wrong array was causing 'should record style mut…

…ations with multiple child nodes and replay them correctly' test to fail. I haven't looked into things more deeply than that the test was complaining about missing .length after `replayer.pause(1000);`

packages/rrweb-snapshot/src/rebuild.ts

@@ -114,7 +114,7 @@ export function applyCssSplits(
     const childTextNode = childTextNodes[i];
     if (!hackCss) {
       childTextNode.textContent = cssTextSplits[i];
-    } else if (i < childTextNodes.length - 1) {
+    } else if (i < cssTextSplits.length - 1) {
       let endIndex = startIndex;
       let endSearch = cssTextSplits[i + 1].length;