Switched unlock to defer in newAddrConn (#5556)

clientconn.go

@@ -712,8 +712,8 @@ func (cc *ClientConn) newAddrConn(addrs []resolver.Address, opts balancer.NewSub
 	ac.ctx, ac.cancel = context.WithCancel(cc.ctx)
 	// Track ac in cc. This needs to be done before any getTransport(...) is called.
 	cc.mu.Lock()
+	defer cc.mu.Unlock()
 	if cc.conns == nil {
-		cc.mu.Unlock()
 		return nil, ErrClientConnClosing
 	}
 
@@ -732,7 +732,6 @@ func (cc *ClientConn) newAddrConn(addrs []resolver.Address, opts balancer.NewSub
 	})
 
 	cc.conns[ac] = struct{}{}
-	cc.mu.Unlock()
 	return ac, nil
 }