[Bug 39440] embedded (XEMBED) windows are blank

https://bugs.winehq.org/show_bug.cgi?id=39440

--- Comment #3 from Sebastian Lackner  ---
Your embedder code does not following the XEMBED specification correctly. The
specification says, that the embedder is responsible to map/unmap the client,
depending on the XEMBED_MAPPED property:

--- snip ---
XEMBED_MAPPED
If set the client should be mapped. The embedder must track the flags field by
selecting for PropertyNotify events on the client and map and unmap the client
appropriately. (The embedder can leave the client unmapped when this bit is
set, but should immediately unmap the client upon detecting that the bit has
been unset.)

Rationale: the reason for using this bit rather than MapRequest events is so
that the client can reliably control it's map state before the inception of the
protocol without worry that the client window will become visible as a child of
the root window.
--- snip ---