xfreerdp: Fix disappearing rail windows.

Rail windows currently disappear on resize and on implicit resize
(calc changing view type from standard to scientific).

The bitmask that we send to XCreateWindow() must match the actual
attributes that we are sending (see xf_create_window()).
Because of this we were unintentionally zeroing out some of the
window attributes rather than using their default values.
Merge pull request #1704 from dbungert/rail

xfreerdp: Fix disappearing rail windows.