Skip headers on errors.

This didn't make any sense and should never have been commited.

bin/varnishd/cache/cache_http.c

@@ -806,7 +806,7 @@ http_Merge(const struct http *fm, struct http *to, int not_ce)
 	for (v = HTTP_HDR_FIRST; v < to->nhd; v++) {
 		p = strchr(to->hd[v].b, ':');
 		if (!p)
-			p = 0;
+			continue;
 		u = http_findhdr(fm, p - to->hd[v].b, to->hd[v].b);
 		if (u)
 			fm->hdf[u] &= ~HDF_MARKER;