backends/x11: fix colormap leak
If we change the backend the colormap will get leak, the colormap should be released with xcb_free_colormap before the window destoryed.
Signed-off-by: Chaojiang Luo luochaojiang@uniontech.com
(cherry picked from commit 1747518f)
Co-authored-by: Chaojiang Luo luochaojiang@uniontech.com