Fix a potential use-after-free following an OOM in sqlite3ParserAddCleanup()

and add a mechanism to detect situations where this might occur in the
future.

FossilOrigin-Name: 38ef8ab9830e12acd2c710e113939b1f8dced02612c6933c37a3c948a4030d0a

src/select.c

@@ -4143,6 +4143,7 @@ static int flattenSubquery(
       sqlite3ParserAddCleanup(pToplevel, 
          (void(*)(sqlite3*,void*))sqlite3DeleteTable,
          pTabToDel);
+      testcase( pToplevel->earlyCleanup );
     }else{
       pTabToDel->nTabRef--;
     }
@@ -4865,6 +4866,7 @@ void sqlite3WithPush(Parse *pParse, With *pWith, u8 bFree){
       sqlite3ParserAddCleanup(pParse, 
          (void(*)(sqlite3*,void*))sqlite3WithDelete,
          pWith);
+      testcase( pParse->earlyCleanup );
     }
   }
 }