Bug 1541: Failure when using parallel background transfers

https://winscp.net/tracker/1541

Source commit: 28cd46978aad584543cf719efddd8aa6d049ba6c

source/core/Terminal.cpp

@@ -912,6 +912,7 @@ bool TParallelOperation::CheckEnd(TCollectedFileList * Files)
 //---------------------------------------------------------------------------
 int TParallelOperation::GetNext(TTerminal * Terminal, UnicodeString & FileName, TObject *& Object, UnicodeString & TargetDir, bool & Dir, bool & Recursed)
 {
+  TGuard Guard(FSection.get());
   int Result = 1;
   TCollectedFileList * Files;
   do