wined3d:context.c Check for a context is added

[Anatoly Lyutin]

We need to check context before than refer it.

Changelog:
    Check for a context is added

-- 
Best regards
	Anatoly Lyutin.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: wined3d-context-nil.patch
Type: text/x-patch
Size: 625 bytes
Desc: not available
Url : http://www.winehq.org/pipermail/wine-patches/attachments/20071205/410309c2/attachment.bin