On Windows, the `flags_internal::ShortProgramInvocationName()`
function usually returns the program name with '.exe' (if the
extension is present in the command line during the program startup).
This fact breaks the checks in the `ContainsHelpshortFlags` filter:
obviously, module names have no .exe in them. Therefore, no defined flags
are shown when the program runs with the --help flag. The program name
should be used in filter without this extension even though it is present.

The unit test has also been updated.

Signed-off-by: Pavel Samolysov <samolisov@gmail.com>