Win32 Vout: after the previous fix of Win32 Vout, the fullscreen mode wasn't kept for the next item. This fixes that.

It closes at least #2119 (on any vertical scaled only subtitle).

Can pl_Hold return NULL ?

p_sys cannot be null here.

This fix the big bug of disappearing of the interface in embedded mode.
(cherry picked from commit 29e96eae)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

(cherry picked from commit 95c173411393f6cae467ab6c4f0e708c443bf5a5)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

(cherry picked from commit cecdd2aa20dc1429741ecef1afe7adc3d1300090)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

(cherry picked from commit 6b67205f)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>