avoid infinite parentage when linking rooms

docs/changelog.txt

@@ -36,6 +36,7 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 ## Fixes
 - `embark-assistant`: fixed order of factors when calculating min temperature
 - `embark-assistant`: improved performance of surveying
+- `quickfort`: creating zones no longer causes eventual crashes
 
 ## Misc Improvements
 - `buildingplan`: set global settings from the ``DFHack#`` prompt: e.g.  ``buildingplan set boulders false``

library/modules/Buildings.cpp

@@ -885,7 +885,7 @@ static void linkRooms(df::building *bld)
             continue;
 
         df::building_extents_type *pext = getExtentTile(room->room, df::coord2d(bld->x1, bld->y1));
-        if (!pext || !*pext)
+        if (!pext || !*pext || room == bld)
             continue;
 
         changed = true;