Increase dialog exit status parsing safety in the locker

This also stops using -1 as auth failed, and moves all failure statuses
to positive numbers.  It looks like Exiting with -1 ends up setting the
status to 255 on exit, but then in the locker, it sees this as 255 and
not -1, since things get coerced into 32-bit integers.

locker/src/screensaver.rs

@@ -1,7 +1,6 @@
 use log::{debug, error, info, trace, warn};
 use std::{
     io::Read,
-    os::unix::process::ExitStatusExt,
     process::{Child, Command, Stdio},
     time::Instant, path::{PathBuf, Path},
 };
@@ -9,7 +8,7 @@ use xcb::{randr, x, Xid, XidNew};
 use xcb_xembed::embedder::Embedder;
 
 use bscreensaver_command::{BCommand, create_command_window};
-use bscreensaver_util::{*, settings::Configuration};
+use bscreensaver_util::{*, dialog::DialogExitStatus, settings::Configuration};
 
 use crate::{
     monitor::*,
@@ -308,17 +307,24 @@ impl<'a> Screensaver<'a> {
                     warn!("Failed to check unlock dialog's status: {}", err);
                     self.unlock_dialog = Some(unlock_dialog);
                 },
-                Ok(Some(status)) if status.success() => {
-                    info!("Authentication succeeded");
-                    self.unlock_screen()?;
-                }
-                Ok(Some(status)) if status.signal().is_some() => {
-                    if let Some(signum) = status.signal() {
-                        warn!("Unlock dialog crashed with signal {}", signum);
+                Ok(Some(status)) => {
+                    let ok = match DialogExitStatus::try_from(status) {
+                        Ok(result) => {
+                            info!("{}", result);
+                            result == DialogExitStatus::AuthSucceeded
+                        },
+                        Err(error) => {
+                            warn!("{}", error);
+                            false
+                        },
+                    };
+
+                    if ok {
+                        self.unlock_screen()?;
+                    } else {
+                        self.hide_cursor();
                     }
-                    self.hide_cursor();
                 },
-                Ok(Some(_)) => self.hide_cursor(),  // auth failed, dialog has quit, do nothing
                 Ok(None) => self.unlock_dialog = Some(unlock_dialog),  // dialog still running
             }
         }