Crash if try to execute on Windows workflow example with Spades

Version 39.0: on Windows
Crash report http://api.ugene.net/tools/ugenecrashes/index.php?id=24222

Scenario:

1. Load workflow sample Read Illumina PE Reads with Spades (SPAdes tool is available on macOS and Linux operating systems only.)
2. Add all settings and push Validate and get message: "Add spades in the Application settings"
3. Open External Tool and add any file as executable Spades. Get message: ""It is possible that the specified executable file is invalid"
4. In Workflow push Validate button
   Crash:

   U2Lang.dll!U2::WorkflowUtils::validate(U2::Workflow::Schema const &,QList &) [WorkflowUtils.cpp : 307 + 0x1d]
   

5. Need to lock button for adding Spades in External tool for Windows.
6. Need to add message in the workflow execution, that "SPAdes tool is available on macOS and Linux operating systems only".