In egl mode the scale_x and scale_y variables are not set, so the
scaling logic in the mouse motion event handler does not work.

Fix that.  Also scale the cursor position in gd_egl_cursor_position().

Reported-by: Chen Zhang <tgfbeta@icloud.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Tested-by: Chen Zhang <tgfbeta@icloud.com>
Message-id: 20181107074949.13805-1-kraxel@redhat.com