Bug 2093: Failure when starting parallel FTP background transfers

https://winscp.net/tracker/2093
(cherry picked from commit c9059f077691e33055443231eea52e4cab571ebc)

Source commit: 64e10cde3c00ba5816a60352ebac810a47b6a690

libs/mfc/source/except.cpp

@@ -45,7 +45,7 @@ static char THIS_FILE[] = __FILE__;
 // AFX_EXCEPTION_CONTEXT (thread global state)
 
 // WINSCP
-AFX_EXCEPTION_CONTEXT m_exceptionContext;
+AFX_EXCEPTION_CONTEXT __thread m_exceptionContext;
 
 inline AFX_EXCEPTION_CONTEXT* AfxGetExceptionContext()
 {