Fix regression for timed-out stream cleanups

If a stream is already timed-out, then either the data or error stream
may be `nil`. This would cause a segmentation fault, which is now
covered with this patch.

Signed-off-by: Sascha Grunert <sgrunert@redhat.com>

staging/src/k8s.io/apimachinery/pkg/util/httpstream/spdy/connection.go

@@ -123,7 +123,10 @@ func (c *connection) Close() error {
 func (c *connection) RemoveStreams(streams ...httpstream.Stream) {
 	c.streamLock.Lock()
 	for _, stream := range streams {
-		delete(c.streams, stream.Identifier())
+		// It may be possible that the provided stream is nil if timed out.
+		if stream != nil {
+			delete(c.streams, stream.Identifier())
+		}
 	}
 	c.streamLock.Unlock()
 }

staging/src/k8s.io/apimachinery/pkg/util/httpstream/spdy/connection_test.go

@@ -323,6 +323,9 @@ func TestConnectionRemoveStreams(t *testing.T) {
 	// remove all existing
 	c.RemoveStreams(stream0, stream1)
 
+	// remove nil stream should not crash
+	c.RemoveStreams(nil)
+
 	if len(c.streams) != 0 {
 		t.Fatalf("should not have any streams, has %d", len(c.streams))
 	}