Clouds cannot have engravings in them

... so delete the existing engraving if a cloud is put on the map.

doc/fixes3-7-0.txt

@@ -1277,6 +1277,7 @@ lightning has a small chance of melting iron bars
 make spell menu work with repeat
 when attempting to look up a named fruit in data.base, try harder
 set and check mon->mstate flags more consistently
+fix sanity error when cloud was created over an engraving
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

src/objnam.c

@@ -3384,6 +3384,7 @@ wizterrainwish(struct _readobjnam_data *d)
         lev->typ = CLOUD;
         lev->flags = 0;
         pline("A cloud.");
+        del_engr_at(x, y);
         madeterrain = TRUE;
     } else if (!BSTRCMPI(bp, p - 4, "door")
                || (d->doorless && !BSTRCMPI(bp, p - 7, "doorway"))) {

src/sp_lev.c

@@ -5255,6 +5255,8 @@ sel_set_ter(coordxy x, coordxy y, genericptr_t arg)
         levl[x][y].horizontal = 1;
     } else if (splev_init_present && levl[x][y].typ == ICE) {
         levl[x][y].icedpool = icedpools ? ICED_POOL : ICED_MOAT;
+    } else if (levl[x][y].typ == CLOUD) {
+        del_engr_at(x, y); /* clouds cannot have engravings */
     }
 }