BUG/MINOR: ssl_ckch: Fix possible uninitialized value in show_cert I/O handler

Commit 3e94f5d4b ("BUG/MINOR: ssl_ckch: Dump cert transaction only once if
show command yield") introduced a regression leading to a build error
because of a possible uninitialized value. It is now fixed.

This patch must be backported as far as 2.2.
diff --git a/src/ssl_ckch.c b/src/ssl_ckch.c
index 80853c6..5dbd3a5 100644
--- a/src/ssl_ckch.c
+++ b/src/ssl_ckch.c
@@ -1301,7 +1301,7 @@
 	struct show_cert_ctx *ctx = appctx->svcctx;
 	struct buffer *trash = alloc_trash_chunk();
 	struct ebmb_node *node;
-	struct ckch_store *ckchs;
+	struct ckch_store *ckchs = NULL;
 
 	if (trash == NULL)
 		return 1;