[qfvis] Reset portal status after base vis

This fixes the mightsee updates never occurring, but it doesn't make a
huge difference (though I suppose it might have back in the 90s, or with
a different map).

tools/qfvis/source/qfvis.c

@@ -935,6 +935,9 @@ CalcVis (void)
 
 	printf ("Thread count: %d\n", options.threads);
 	BasePortalVis ();
+	for (i = 0; i < 2 * numportals; i++) {
+		portals[i].status = stat_none;
+	}
 	CalcPortalVis ();
 
 	// assemble the leaf vis lists by oring and compressing the portal lists