Make sure that no decrypted text gets stuck in the plaintext buffer

sdk/lib/io/secure_socket.dart

Index: sdk/lib/io/secure_socket.dart
diff --git a/sdk/lib/io/secure_socket.dart b/sdk/lib/io/secure_socket.dart
index c9d46de6a01a3892116788fd53dd0d137768e242..62ecb4d6e427e196dc17c55f235d69d4b065c6e4 100644
--- a/sdk/lib/io/secure_socket.dart
+++ b/sdk/lib/io/secure_socket.dart
@@ -404,11 +404,12 @@ class _RawSecureSocket extends Stream<RawSocketEvent>
 
   void set readEventsEnabled(bool value) {
     _readEventsEnabled = value;
-    if (_socketClosedRead) {
-      if (value) {
-        // We have no underlying socket to set off read events.
-        Timer.run(_readHandler);
-      }
+    if (value &&
+        ((_secureFilter != null &&
+          _secureFilter.buffers[READ_PLAINTEXT].length > 0) ||
+         _socketClosedRead)) {
+      // We might not have no underlying socket to set off read events.
+      Timer.run(_readHandler);
     }
   }