thermald, redbear-upower: probe ACPI surface via read_dir

Both daemons previously checked /scheme/acpi/thermal (thermald) and
/scheme/acpi/power (redbear-upower) existence with Path::exists or
is_dir, which use stat/lstat. On Redox these syscalls can return
errors for scheme paths even when the scheme IS registered, leading
to false 'unavailable' warnings even after the new acpid thermal/
power directories were added.

Use fs::read_dir (which already worked for actual zone enumeration)
as the existence probe instead. The match expression intentionally
calls read_dir to discard the iterator and keep only the Result;
using ? here would break the warn-once pattern.

local/recipes/system/redbear-upower/source/src/main.rs

@@ -211,7 +211,9 @@ impl PowerRuntime {
     }
 
     fn available(&self) -> bool {
-        self.root.exists()
+        // is_dir() uses stat which misbehaves on Redox schemes; read_dir
+        // is the only reliable existence probe.
+        self.root.read_dir().is_ok()
     }
 
     fn adapter_dir(&self, id: &str) -> PathBuf {

local/recipes/system/thermald/source/src/main.rs

@@ -534,7 +534,10 @@ fn monitor_loop(shared: Arc<RwLock<ThermalState>>) -> ! {
     let mut warned_missing_surface = false;
 
     loop {
-        if !Path::new(ACPI_THERMAL_ROOT).exists() {
+        // is_dir() / exists() use stat/lstat which return errors on
+        // Redox schemes; read_dir is the only reliable existence probe.
+        let surface_available = fs::read_dir(ACPI_THERMAL_ROOT).is_ok();
+        if !surface_available {
             if !warned_missing_surface {
                 warn!(
                     "{} is unavailable; thermald will keep polling and serve an empty thermal surface",