Bug 1484: Failure when pressing Calculate button on Properties dialog, while another calculation is already in progress

https://winscp.net/tracker/1484

Source commit: 4904744292bf1037aa6ca2d1d50b0e2bac45b3b8

source/forms/Properties.cpp

@@ -572,6 +572,7 @@ void __fastcall TPropertiesDialog::CalculateSizeButtonClick(
   DebugAssert(FOnCalculateSize != NULL);
 
   bool DoClose = false;
+  Enabled = false;
   try
   {
     __int64 Size;
@@ -582,6 +583,7 @@ void __fastcall TPropertiesDialog::CalculateSizeButtonClick(
   }
   __finally
   {
+    Enabled = true;
     if (DoClose)
     {
       Close();