tasks: move read of system time into halt block

This ensures that the system time shown is consistent with the one that
was visible to the tasks at the time the snapshot was taken.

Author: cbiffle

cmd/tasks/src/lib.rs

@@ -219,7 +219,6 @@ pub fn print_tasks(
 ) -> Result<()> {
     let (base, task_count) = hubris.task_table(core)?;
     log::debug!("task table: {:#x?}, count: {}", base, task_count);
-    let ticks = if core.is_net() { None } else { Some(hubris.ticks(core)?) };
 
     let task_t = hubris.lookup_struct_byname("Task")?;
     let save = task_t.lookup_member("save")?.offset;
@@ -237,6 +236,9 @@ pub fn print_tasks(
     loop {
         core.halt()?;
 
+        let ticks =
+            if core.is_net() { None } else { Some(hubris.ticks(core)?) };
+
         let cur = hubris.current_task(core)?;
         let task_dump = hubris.task_dump();