BUG/MINOR: ssl: init tmp chunk correctly in ssl_sock_load_sctl_from_file()

Use chunk_inistr() for a chunk initialisation in
ssl_sock_load_sctl_from_file() instead of a manual initialisation which
was not initialising head.

Fix issue #1073.

Must be backported as far as 2.2

(cherry picked from commit 8d67394f6915c6d2db40bc1e9593fd392827da8d)
Signed-off-by: Willy Tarreau <w@1wt.eu>
diff --git a/src/ssl_ckch.c b/src/ssl_ckch.c
index 4a85a5d..1d7f409 100644
--- a/src/ssl_ckch.c
+++ b/src/ssl_ckch.c
@@ -101,9 +101,7 @@
 	struct buffer *sctl;
 
 	if (buf) {
-		tmp.area = buf;
-		tmp.data = strlen(buf);
-		tmp.size = tmp.data + 1;
+		chunk_initstr(&tmp, buf);
 		src = &tmp;
 	} else {
 		fd = open(sctl_path, O_RDONLY);