Set current certificate to selected certificate.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2637)

ssl/t1_lib.c

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 3e00cdb..6aa4dec 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -2444,6 +2444,7 @@
         }
     }
     s->s3->tmp.cert = &s->cert->pkeys[idx];
+    s->cert->key = s->s3->tmp.cert;
     s->s3->tmp.sigalg = lu;
     return 1;
 }