Make (level) teleporting clear monster movement tracking

src/dog.c

@@ -325,8 +325,7 @@ boolean with_you;
     xyflags = mtmp->mtrack[0].y;
     xlocale = mtmp->mtrack[1].x;
     ylocale = mtmp->mtrack[1].y;
-    mtmp->mtrack[0].x = mtmp->mtrack[0].y = 0;
-    mtmp->mtrack[1].x = mtmp->mtrack[1].y = 0;
+    memset(mtmp->mtrack, MTSZ, sizeof(coord));
 
     if (mtmp == u.usteed)
         return; /* don't place steed on the map */

src/teleport.c

@@ -980,6 +980,7 @@ register int x, y;
         }
     }
 
+    memset(mtmp->mtrack, MTSZ, sizeof(coord));
     place_monster(mtmp, x, y); /* put monster down */
     update_monster_region(mtmp);