Pcbnew: fix lock file bug on windows.

The lock file code would reset the lock file every other time the same
board file was opened in Pcbnew in the stand alone mode.  This created
the perfect toggle switch causing the board to be reloaded every other
time the same board was selected.

Please note that wxSingleInstanceChecker is broken on Linux and most
likely MacOS as well due to a bug in wxWidgets.  On these platforms,
the already opened file is reopened rather than displaying a warning
that the file is already opened.

Fixes lp:1777599

https://bugs.launchpad.net/kicad/+bug/1777599

pcbnew/files.cpp

@@ -45,6 +45,7 @@
 #include <kiway.h>
 #include <kiway_player.h>
 #include <trace_helpers.h>
+#include <lockfile.cpp>
 
 #include <pcbnew.h>
 #include <pcbnew_id.h>
@@ -412,13 +413,17 @@ bool PCB_EDIT_FRAME::OpenProjectFiles( const std::vector<wxString>& aFileSet, in
     // We insist on caller sending us an absolute path, if it does not, we say it's a bug.
     wxASSERT_MSG( wxFileName( fullFileName ).IsAbsolute(), wxT( "Path is not absolute!" ) );
 
-    if( !LockFile( fullFileName ) )
+    std::unique_ptr<wxSingleInstanceChecker> lockFile = ::LockFile( fullFileName );
+
+    if( !lockFile )
     {
         wxString msg = wxString::Format( _( "PCB file \"%s\" is already open." ), fullFileName );
         DisplayError( this, msg );
         return false;
     }
 
+    m_file_checker.reset( lockFile.release() );
+
     if( GetScreen()->IsModify() && !GetBoard()->IsEmpty() )
     {
         if( !HandleUnsavedChanges( this, _( "The current PCB has been modified.  Save changes?" ),