Simplest fix for #8185: SIGSEGV in Firebird 5.0.0.1306 embedded during update on cursor - disallow caching for positioned updates/deletes

Author: dyemanov

src/dsql/DsqlRequests.cpp

@@ -177,6 +177,8 @@ void DsqlRequest::destroy(thread_db* tdbb, DsqlRequest* dsqlRequest)
 	{
 		childStatement->addFlags(DsqlStatement::FLAG_ORPHAN);
 		childStatement->setParentRequest(nullptr);
+		childStatement->setParentDbKey(nullptr);
+		childStatement->setParentRecVersion(nullptr);
 
 		// hvlad: lines below is commented out as
 		// - child is already unlinked from its parent request

src/dsql/dsql.cpp

@@ -620,7 +620,11 @@ static RefPtr<DsqlStatement> prepareStatement(thread_db* tdbb, dsql_dbb* databas
 		if (!isInternalRequest && dsqlStatement->mustBeReplicated())
 			dsqlStatement->setOrgText(text, textLength);
 
-		if (isStatementCacheActive && dsqlStatement->isDml())
+		const bool basedOnCursor =
+			(dsqlStatement->getType() & (DsqlStatement::TYPE_UPDATE_CURSOR |
+										 DsqlStatement::TYPE_DELETE_CURSOR));
+
+		if (isStatementCacheActive && dsqlStatement->isDml() && !basedOnCursor)
 		{
 			database->dbb_statement_cache->putStatement(tdbb,
 				textStr, clientDialect, isInternalRequest, dsqlStatement);