Fixed a compile warning introduced by 01e2a5bcdd8f.

On systems with OpenSSL that has NPN support but lacks
ALPN support, some compilers emitted a warning about
possibly uninitialized "data" variable.

src/http/ngx_http_request.c

diff --git a/src/http/ngx_http_request.c b/src/http/ngx_http_request.c
index a882cca..a0e6fad 100644
--- a/src/http/ngx_http_request.c
+++ b/src/http/ngx_http_request.c
@@ -713,11 +713,8 @@
         const unsigned char     *data;
         static const ngx_str_t   spdy = ngx_string(NGX_SPDY_NPN_NEGOTIATED);
 
-        len = 0;
-
 #ifdef TLSEXT_TYPE_application_layer_protocol_negotiation
         SSL_get0_alpn_selected(c->ssl->connection, &data, &len);
-#endif
 
 #ifdef TLSEXT_TYPE_next_proto_neg
         if (len == 0) {
@@ -725,6 +722,10 @@
         }
 #endif
 
+#else /* TLSEXT_TYPE_next_proto_neg */
+        SSL_get0_next_proto_negotiated(c->ssl->connection, &data, &len);
+#endif
+
         if (len == spdy.len && ngx_strncmp(data, spdy.data, spdy.len) == 0) {
             ngx_http_spdy_init(c->read);
             return;