task: optimize for common case of single following Task

If there is only one Task in the post exec queue, we can
simply insert that Task instead of creating a task to hold
a post exec queue of one item.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

lib/task.cc

@@ -199,7 +199,11 @@ namespace crucible {
 			tlcc->m_local_queue.splice(tlcc->m_local_queue.begin(), queue);
 		} else {
 			// We are not executing under a TaskConsumer.
-			// Create a new task to wrap our post-exec queue,
+			// If there is only one task, then just insert it at the front of the queue.
+			if (queue.size() == 1) {
+				TaskMasterState::push_front(queue);
+			} else {
+				// If there are multiple tasks, create a new task to wrap our post-exec queue,
 				// then push it to the front of the global queue using normal locking methods.
 				TaskStatePtr rescue_task(make_shared<TaskState>("rescue_task", [](){}));
 				swap(rescue_task->m_post_exec_queue, queue);
@@ -207,6 +211,7 @@ namespace crucible {
 				TaskMasterState::push_front(tq_one);
 			}
 		}
+	}
 
 	TaskState::~TaskState()
 	{