win32: remove try-catch block of GetModuleFileNameEx (issue2480)
According to the API document, GetModuleFileName is the preferred way to
retrieve the filename of the current process. So we shouldn't try
GetModuleFileName'Ex' first.
Previously system_rcpath_win32() happened to return unicode paths due to
GetModuleFileNameEx (issue2480). This problem is fixed as GetModuleFileName
never return unicode.