Handle leak in screen.c

[sminux]

Handle leak detected by svace static analyze tool

Describe the bug
The handle 'fd' is created at

x11vnc/src/screen.c

Line 1778 in a61f364

fd = open(tmp, O_WRONLY);

by calling function 'open' and lost at

x11vnc/src/screen.c

Line 2513 in a61f364

return raw_fb_image;

To Reproduce

Expected Behavior

Screenshots

Desktop (please complete the following information):

• Debian and latest version:

Additional context