[#301] rpc: Make client stream initialization get cancelled by dial timeout

* `c.conn` may be already invalidated but the rpc client can't detect this.
  `NewStream` may hang trying to open a stream with invalidated connection.
  Using timer with `dialTimeout` for `NewStream` fixes this problem.

Signed-off-by: Airat Arifullin <a.arifullin@yadro.com>

api/rpc/client/init.go

@@ -52,6 +52,7 @@ func (c *Client) Init(info common.CallMethodInfo, opts ...CallOption) (MessageRe
 	}
 
 	ctx, cancel := context.WithCancel(prm.ctx)
+	defer cancel()
 
 	// `conn.NewStream` doesn't check if `conn` may turn up invalidated right before this invocation.
 	// In such cases, the operation can hang indefinitely, with the context timeout being the only
@@ -76,13 +77,15 @@ func (c *Client) Init(info common.CallMethodInfo, opts ...CallOption) (MessageRe
 	}()
 	select {
 	case <-dialTimeoutTimer.C:
-		cancel()
-		return nil, context.Canceled
+		select {
+		case <-newStreamCh:
+		default:
+			return nil, context.Canceled
+		}
 	case <-newStreamCh:
 	}
 
 	if err != nil {
-		cancel()
 		return nil, err
 	}