[BUG, BACKEND: D3D9] Clipboard paste broken for D3D9 backend

[PavelSharp]

The clipboard paste functionality in the Nuklear D3D9 backend is broken due to an incorrect check when opening the clipboard. In the current implementation of nk_d3d9_clipboard_paste:

Nuklear/demo/d3d9/nuklear_d3d9.h

Lines 484 to 486 in fcd64f8

	if (!IsClipboardFormatAvailable(CF_UNICODETEXT) && OpenClipboard(NULL)) {
	return;
	}

This differs from other DirectX backends (D3D11, D3D12), where the paste function works correctly and this bug does not occur.

As enhancement. However, it is worth noting that even in those backends the order of operations is somewhat questionable: they call IsClipboardFormatAvailable before opening the clipboard with OpenClipboard(NULL).