crash in windows tk_getSaveFile

When using tk_getSaveFile, if the user manoeuvers
to a directory which contains a lot of
files/directories, it takes a few seconds for the
dialog to display everything (and the "searching
flashlight" is shown sweeping back and forth).

If, during those seconds, the user decides to click
on 'save' (a perfectly reasonable thing to do if the
user wants to save the file in that directory), wish
exits immediately, with no warning or error
message at all.