winex11.drv: Recreate gl_drawable for top-level windows as non-top level when clipping for child windows is required.

Prevent creating a gl_drawable for a window as type DC_GL_WINDOW if
there are known children of the window, since DC_GL_WINDOW does not
support clipping.

Recreate a gl_drawable that was previously create as type DC_GL_WINDOW
when a child is encountered.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=15232Signed-off-by: Micah N Gorrell <mgorrell@codeweavers.com>
Signed-off-by: Ken Thomases <ken@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>