virtmgr: Log failed sysprop read for custom DP

Instead of silently map the Err(_) from system_properties::read() to a
default value, log the failure first.

Test: m virtmgr
Change-Id: I688b6444dc5f22283e45d3298aaa48dafcea95dd
diff --git a/virtualizationmanager/src/debug_config.rs b/virtualizationmanager/src/debug_config.rs
index 6b495aa..cb7f5d0 100644
--- a/virtualizationmanager/src/debug_config.rs
+++ b/virtualizationmanager/src/debug_config.rs
@@ -162,7 +162,13 @@
             _ => DebugLevel::NONE,
         };
 
-        match system_properties::read(CUSTOM_DEBUG_POLICY_OVERLAY_SYSPROP).unwrap_or_default() {
+        let dp_sysprop = system_properties::read(CUSTOM_DEBUG_POLICY_OVERLAY_SYSPROP);
+        let custom_dp = dp_sysprop.unwrap_or_else(|e| {
+            warn!("Failed to read sysprop {CUSTOM_DEBUG_POLICY_OVERLAY_SYSPROP}: {e}");
+            Default::default()
+        });
+
+        match custom_dp {
             Some(path) if !path.is_empty() => {
                 match Self::from_custom_debug_overlay_policy(debug_level, Path::new(&path)) {
                     Ok(debug_config) => {