Fix a segfault when re-using wait set (#282)

Author: nnmm

rclrs/src/lib.rs

@@ -46,7 +46,7 @@ pub use wait::*;
 ///
 /// [1]: crate::RclReturnCode
 pub fn spin_once(node: &Node, timeout: Option<Duration>) -> Result<(), RclrsError> {
-    let mut wait_set = WaitSet::new_for_node(node)?;
+    let wait_set = WaitSet::new_for_node(node)?;
     let ready_entities = wait_set.wait(timeout)?;
 
     for ready_subscription in ready_entities.subscriptions {

rclrs/src/wait.rs

@@ -321,7 +321,7 @@ impl WaitSet {
     /// This list is not comprehensive, since further errors may occur in the `rmw` or `rcl` layers.
     ///
     /// [1]: std::time::Duration::ZERO
-    pub fn wait(&mut self, timeout: Option<Duration>) -> Result<ReadyEntities, RclrsError> {
+    pub fn wait(mut self, timeout: Option<Duration>) -> Result<ReadyEntities, RclrsError> {
         let timeout_ns = match timeout.map(|d| d.as_nanos()) {
             None => -1,
             Some(ns) if ns <= i64::MAX as u128 => ns as i64,