Disable graphical debug only once writing to the fd

This allows obtaining an fd for this before calling setrens while doing
the actual disabling after calling it.

src/scheme/debug.rs

@@ -61,12 +61,7 @@ impl KernelScheme for DebugScheme {
 
             "no-preserve" => SpecialFds::NoPreserve as usize,
 
-            "disable-graphical-debug" => {
-                #[cfg(feature = "graphical_debug")]
-                graphical_debug::fini();
-
-                SpecialFds::DisableGraphicalDebug as usize
-            }
+            "disable-graphical-debug" => SpecialFds::DisableGraphicalDebug as usize,
 
             #[cfg(feature = "profiling")]
             p if p.starts_with("profiling-") => {
@@ -165,6 +160,13 @@ impl KernelScheme for DebugScheme {
             return Ok(1);
         }
 
+        if handle.num == SpecialFds::DisableGraphicalDebug as usize {
+            #[cfg(feature = "graphical_debug")]
+            graphical_debug::fini();
+
+            return Ok(0);
+        }
+
         if handle.num != SpecialFds::Default as usize
             && handle.num != SpecialFds::NoPreserve as usize
         {