st/nine: Prevent crash in GetRenderTargetData
st/nine: Prevent crash in GetRenderTargetData

Return error instead of crashing on source surfaces
with format D3DFMT_NULL.

Fix for issue #236.

Tested on Windows 7.

Signed-off-by: Patrick Rudolph <2af63f351b8bda7baf3a287b873bcd3ca66a59bb@das-labor.org>
Reviewed-by: Axel Davy <2b6ef604b998fb81662f85c329e4fc020eae8e5d@ens.fr>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler