BUG/MINOR: mux-h1: Fix processing of "Connection: " header on outgoing messages

in h1_process_output(), before formatting the headers, we need to find and check
the "Connection: " header to update the connection mode. But, the context used
to do so was not correctly initialized. We must explicitly set ctx.value to NULL
to be sure to rescan the current header.
diff --git a/src/mux_h1.c b/src/mux_h1.c
index bade571..1ceac12 100644
--- a/src/mux_h1.c
+++ b/src/mux_h1.c
@@ -1219,6 +1219,7 @@
 					 * right one.
 					 */
 					ctx.blk = blk;
+					ctx.value = ist(NULL);
 					if (http_find_header(chn_htx, n, &ctx, 1))
 						goto process_hdr;
 					h1_process_conn_mode(h1s, h1m, NULL, &v);