x11/slop: unbreak with libglvnd >= 1.3.4

src/framebuffer.cpp:55:9: error: use of undeclared identifier 'XDestroyImage'; did you mean 'XDestroyIC'?

XDestroyImage( image );
^~~~~~~~~~~~~
XDestroyIC

/usr/local/include/X11/Xlib.h:3867:13: note: 'XDestroyIC' declared here
extern void XDestroyIC(

^

src/framebuffer.cpp:55:24: error: cannot initialize a parameter of type 'XIC' (aka '_XIC *') with an lvalue of type 'XImage *' (aka '_XImage *')

XDestroyImage( image );
               ^~~~~

/usr/local/include/X11/Xlib.h:3869:1: note: passing argument to parameter here
);
^

PR: 258269
Reported by: antoine (via exp-run)