crypto/tls: fix a testing deadlock that occurs on a TLS protocol error

A Go routine was, on an error, returning without sending a message on its
signaling channel, so the main program was blocking forever waiting for
a message that was never sent. Found while breaking crypto/tls.

Change-Id: Id0b3c070a27cabd852f74e86bb9eff5c66b86d28
GitHub-Last-Rev: 4d84fb8
GitHub-Pull-Request: #53216
Reviewed-on: https://go-review.googlesource.com/c/go/+/410274
Auto-Submit: Sean Liao <[email protected]>
Reviewed-by: Roland Shoemaker <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Sean Liao <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: eay

src/crypto/tls/handshake_server_test.go

@@ -236,7 +236,6 @@ func TestRenegotiationExtension(t *testing.T) {
 		n, err := c.Read(buf)
 		if err != nil {
 			t.Errorf("Server read returned error: %s", err)
-			return
 		}
 		c.Close()
 		bufChan <- buf[:n]