The sqlite3_close() interface returns SQLITE_OK even if there are outstanding

sqlite3_stmt and sqlite3_backup objects.  The connection becomes a zombie.
Resource deallocation is deferred until the last sqlite3_stmt or 
sqlite3_backup object closes.  This is intended to help SQLite play nicer
with garbage collectors.

FossilOrigin-Name: e276a02b7f54e804caa553dca99023416a415e1c

src/vdbeaux.c

@@ -2469,6 +2469,7 @@ void sqlite3VdbeDelete(Vdbe *p){
 
   if( NEVER(p==0) ) return;
   db = p->db;
+  assert( sqlite3_mutex_held(db->mutex) );
   if( p->pPrev ){
     p->pPrev->pNext = p->pNext;
   }else{