MINOR: httpclient: add the EOH when no headers where provided

httpclient_req_gen() now adds the end of headers block when no header
was provided, which avoid adding it manually.
diff --git a/src/http_client.c b/src/http_client.c
index debdee5..69297e1 100644
--- a/src/http_client.c
+++ b/src/http_client.c
@@ -283,8 +283,13 @@
 		goto error;
 
 	/* add the headers and EOH */
-	if (hdrs && !htx_add_all_headers(htx, hdrs))
-		goto error;
+	if (hdrs) {
+		if (!htx_add_all_headers(htx, hdrs))
+			goto error;
+	} else {
+		if (!htx_add_endof(htx, HTX_BLK_EOH))
+			goto error;
+	}
 
 	htx->flags |= HTX_FL_EOM;