fix an impossible() on pick-up from stomach

doc/fixes3-7-0.txt

@@ -2234,6 +2234,9 @@ cursed magic whistle could teleport hero on no-teleport levels
 give a brief explanation when receiving a wish for acquiring the Amulet
 teleportation traps no longer teleport you on levels made temporarily
 	no-teleport by the presence of a monster
+an attempt to pick up an object from a monster's stomach would trigger
+	an impossible() in newsym() due to object having no ox,oy coordinates
+	set; set the coordinates to the monster's at the start of pick_obj()
 
 
 Fixes to 3.7.0-x Platform and/or Interface Problems Exposed Via git Repository

src/pickup.c

@@ -1897,8 +1897,24 @@ struct obj *
 pick_obj(struct obj *otmp)
 {
     struct obj *result;
-    int ox = otmp->ox, oy = otmp->oy;
+    int ox, oy;
-    boolean robshop = (!u.uswallow && otmp != uball && costly_spot(ox, oy));
+    boolean robshop = FALSE;
+
+    if (otmp->ox == 0 && otmp->oy == 0) {
+        if (u.uswallow && u.ustuck && otmp->where == OBJ_MINVENT
+            && otmp->ocarry == u.ustuck) {
+            otmp->ox = u.ustuck->mx;
+            otmp->oy = u.ustuck->my;
+        } else {
+            /* this will be a problem for newsym below */
+            impossible("otmp has no location coordinates <%d, %d> where=%d.",
+                       otmp->ox, otmp->oy, otmp->where);
+        }
+    }
+
+    ox = otmp->ox;
+    oy = otmp->oy;
+    robshop = (!u.uswallow && otmp != uball && costly_spot(ox, oy));
 
     obj_extract_self(otmp);
     newsym(ox, oy);