[FIXED] Possible stall on shutdown with leafnode setup

If a leafnode connection is accepted but the server is shutdown
before the connection is fully registered, the shutdown would
stall because read and write loop go routine would not be
stopped.

Signed-off-by: Ivan Kozlovic <ivan@synadia.com>

server/leafnode.go

@@ -794,6 +794,14 @@ func (s *Server) createLeafNode(conn net.Conn, remote *leafNodeCfg) *client {
 		}
 	}
 
+	// Keep track in case server is shutdown before we can successfully register.
+	if !s.addToTempClients(c.cid, c) {
+		c.mu.Unlock()
+		c.setNoReconnect()
+		c.closeConnection(ServerShutdown)
+		return nil
+	}
+
 	// Spin up the read loop.
 	s.startGoRoutine(func() { c.readLoop() })
 
@@ -955,6 +963,7 @@ func (s *Server) addLeafNodeConnection(c *client) {
 	s.mu.Lock()
 	s.leafs[cid] = c
 	s.mu.Unlock()
+	s.removeFromTempClients(cid)
 }
 
 func (s *Server) removeLeafNodeConnection(c *client) {
@@ -964,6 +973,7 @@ func (s *Server) removeLeafNodeConnection(c *client) {
 	s.mu.Lock()
 	delete(s.leafs, cid)
 	s.mu.Unlock()
+	s.removeFromTempClients(cid)
 }
 
 type leafConnectInfo struct {