logic: Fixed crashes and halting during indexing

* Fixed CPPSqliteException being thrown due to not properly destructed statement in addError
* Fixed indexer getting stuck after building caches because MessageFinishedParsing was interrupted
* removed Message::cancel() method and all related code

bug id = 105

src/lib/data/PersistentStorage.cpp

@@ -229,7 +229,7 @@ void PersistentStorage::finishInjection()
 	{
 		MessageShowErrors msg(errorCount);
 		msg.setSendAsTask(false);
-		msg.dispatch();
+		msg.dispatchImmediately();
 	}
 	m_preInjectionErrorCount = -1;
 }