MINOR: quic: BUG_ON() SSL errors.

As this QUIC implementation is still experimental, let's BUG_ON()
very important SSL handshake errors.
Also dump the SSL errors before BUG_ON().

src/xprt_quic.c

@@ -1622,6 +1622,8 @@ static inline int qc_provide_cdata(struct quic_enc_level *el,
 
 			TRACE_DEVEL("SSL handshake error",
 			            QUIC_EV_CONN_HDSHK, ctx->conn, &state, &ssl_err);
+			qc_ssl_dump_errors(ctx->conn);
+			BUG_ON(1);
 			goto err;
 		}