Fix a random SSL crash I saw once.

I don't know why this happened, I was debugging another issue. This
should take care of it though.

(cherry picked from commit 64626f682e)

core/io/http_client.cpp

@@ -346,6 +346,12 @@ Error HTTPClient::poll() {
 						} else {
 							// We are already handshaking, which means we can use your already active SSL connection
 							ssl = static_cast<Ref<StreamPeerSSL> >(connection);
+							if (ssl.is_null()) {
+								close();
+								status = STATUS_SSL_HANDSHAKE_ERROR;
+								return ERR_CANT_CONNECT;
+							}
+
 							ssl->poll(); // Try to finish the handshake
 						}