BUG/MINOR: http_ana: clarify connection pointer check on L7 retry

Coverity reports a possible null deref in issue #703. It seems this
cannot happen as in order to have a CF_READ_ERROR we'd need to have
attempted a recv() which implies a conn_stream, thus conn cannot be
NULL anymore. But at least one line tests for conn and the other one
not, which is confusing. So let's add a check for conn before
dereferencing it.

This needs to be backported to 2.1 and 2.0. Note that in 2.0 it's
in proto_htx.c.

(cherry picked from commit ee99aaf1f9bad06475aaf8c5dc3c0986a9899952)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
(cherry picked from commit 148e7c41fcdc5bc4fde65a5a39a6f41d3c48f545)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/src/proto_htx.c b/src/proto_htx.c
index a0ca996..35925c4 100644
--- a/src/proto_htx.c
+++ b/src/proto_htx.c
@@ -1525,7 +1525,7 @@
 			/* Check to see if the server refused the early data.
 			 * If so, just send a 425
 			 */
-			if (conn->err_code == CO_ER_SSL_EARLY_FAILED) {
+			if (conn && conn->err_code == CO_ER_SSL_EARLY_FAILED) {
 				if ((s->be->retry_type & PR_RE_EARLY_ERROR) &&
 				    (si_b->flags & SI_FL_L7_RETRY) &&
 				    do_l7_retry(s, si_b) == 0)