Handle watch events that arrive before plugin start-up

pkg/analysis_server/lib/src/plugin/plugin_manager.dart

Index: pkg/analysis_server/lib/src/plugin/plugin_manager.dart
diff --git a/pkg/analysis_server/lib/src/plugin/plugin_manager.dart b/pkg/analysis_server/lib/src/plugin/plugin_manager.dart
index 11b61997ce1b3e41b264889385044dcde171c1ef..9ceb4c32dab2cc499b33d0ad4b820e8f9d53f649 100644
--- a/pkg/analysis_server/lib/src/plugin/plugin_manager.dart
+++ b/pkg/analysis_server/lib/src/plugin/plugin_manager.dart
@@ -423,7 +423,12 @@ class PluginManager {
       PluginSession session = plugin.currentSession;
       if (session != null &&
           plugin.isAnalyzing(filePath) &&
+          session.interestingFiles != null &&
           session.interestingFiles.any(matches)) {
+        // The list of interesting file globs is `null` if the plugin has not
+        // yet responded to the plugin.versionCheck request. If that happens
+        // then the plugin hasn't had a chance to analyze anything yet, and
+        // hence it does not needed to get watch events.
         event ??= _convertWatchEvent(watchEvent);
         AnalysisHandleWatchEventsParams params =
             new AnalysisHandleWatchEventsParams([event]);