MainWindow: fix ignore WM_SIZE causes statusbar invisible when created

[evangwt]

Fix this issue

As @jackyzy823 mentioned that this commit introduced the bug. And I find this line is the key.

Here are some additional remark from MSDN doc

By default, the DefWindowProc function sends the WM_SIZE and WM_MOVE messages to the window. The WM_SIZE and WM_MOVE messages are not sent if an application handles the WM_WINDOWPOSCHANGED message without calling DefWindowProc. It is more efficient to perform any move or size change processing during the WM_WINDOWPOSCHANGED message without calling DefWindowProc.

[alkanna]

This should be merged, it's working without any issues atm.

[alkanna]

Ping @lxn

[lxn]

Please add yourself to the AUTHORS file, then this can be merged.

[alkanna]

@evangwt

[evangwt]

Please add yourself to the AUTHORS file, then this can be merged.

Thanks for your review, AUTHORS is updated ;)

[lxn]

Thanks!