wined3d: We only need to enable texturing for a target if we're going to draw with it (without a shader).

Also, these enables cause problems if they're done while the context
is setup for blitting.

user32: DrawText handling of 0 counts with string, empty strings and -1 counts with empty string and NULL strings.

This allows the file to be compiled on platforms that don't have the
header file, such as MSVC.

Therefore, declare the structure as user_bstr_t and make wire_bstr_t
be a typedef to a pointer of this type.