Codechange: reference a string by its name, not with "another + 1" (#9517)

It is wrong anyway, as "TINY" normally is at -1. Just weird code.

src/viewport.cpp

@@ -1422,12 +1422,12 @@ static void ViewportAddKdtreeSigns(DrawPixelInfo *dpi)
 		if (Station::IsExpected(st)) {
 			/* Station */
 			ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &st->sign,
-				STR_VIEWPORT_STATION, STR_VIEWPORT_STATION + 1, STR_NULL,
+				STR_VIEWPORT_STATION, STR_VIEWPORT_STATION_TINY, STR_NULL,
 				st->index, st->facilities, (st->owner == OWNER_NONE || !st->IsInUse()) ? COLOUR_GREY : _company_colours[st->owner]);
 		} else {
 			/* Waypoint */
 			ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &st->sign,
-				STR_VIEWPORT_WAYPOINT, STR_VIEWPORT_WAYPOINT + 1, STR_NULL,
+				STR_VIEWPORT_WAYPOINT, STR_VIEWPORT_WAYPOINT_TINY, STR_NULL,
 				st->index, st->facilities, (st->owner == OWNER_NONE || !st->IsInUse()) ? COLOUR_GREY : _company_colours[st->owner]);
 		}
 	}