Skip parallel suspension when checkpoint is nil

The triggering entry in the parallel-suspend path stored
se.Checkpoint into innerCheckpoints unconditionally, while
the sibling loop already guarded otherSE.Checkpoint != nil.
A nil entry would later cause restoreNestedSuspended to
dereference innerCP.AgentName and panic. Apply the same
guard so a malformed SuspendedError falls through to the
regular result-collection path instead of poisoning the
checkpoint map.

Signed-off-by: Aurélien Sibiril <81782+aureliensibiril@users.noreply.github.com>

pkg/agent/run.go

@@ -976,7 +976,7 @@ func executeParallel(
 			continue
 		}
 		se, ok := errors.AsType[*SuspendedError](entry.err)
-		if ok {
+		if ok && se.Checkpoint != nil {
 			innerCheckpoints := make(map[string]*Checkpoint)
 			var completed []CompletedCall