Guard analysis server's getAnalysisResult, must be dart

pkg/analysis_server/lib/src/analysis_server.dart

Index: pkg/analysis_server/lib/src/analysis_server.dart
diff --git a/pkg/analysis_server/lib/src/analysis_server.dart b/pkg/analysis_server/lib/src/analysis_server.dart
index ff6c0c95bac189f7d55e738455d8ff3bac4afedd..8fe0d1849b65ba0c7bab8b4a20c652f23e2457cb 100644
--- a/pkg/analysis_server/lib/src/analysis_server.dart
+++ b/pkg/analysis_server/lib/src/analysis_server.dart
@@ -662,6 +662,10 @@ class AnalysisServer {
    * otherwise in the first driver, otherwise `null` is returned.
    */
   Future<nd.AnalysisResult> getAnalysisResult(String path) async {
+    if (!AnalysisEngine.isDartFileName(path)) {
+      return null;
+    }
+
     try {
       nd.AnalysisDriver driver = getAnalysisDriver(path);
       return await driver?.getResult(path);