Initialize next_proto in s_server - resolves incorrect attempts to free

apps/s_server.c

diff --git a/apps/s_server.c b/apps/s_server.c
index 35f30e4..9359161 100644
--- a/apps/s_server.c
+++ b/apps/s_server.c
@@ -1065,7 +1065,7 @@
         tlsextctx tlsextcbp = {NULL, NULL, SSL_TLSEXT_ERR_ALERT_WARNING};
 # ifndef OPENSSL_NO_NEXTPROTONEG
 	const char *next_proto_neg_in = NULL;
-	tlsextnextprotoctx next_proto;
+	tlsextnextprotoctx next_proto = { NULL, 0};
 	const char *alpn_in = NULL;
 	tlsextalpnctx alpn_ctx = { NULL, 0};
 # endif