fix(controller): "agent task already running" (#1516)

* fix agent task already running bug

* attemp to fix "Current task state not recognized"

* Revert "attemp to fix "Current task state not recognized""

This reverts commit f5cbfe1ebba3f9ed9d9ee8f47d228e2d0117347a.

---------

Co-authored-by: Leo <ifuryst@gmail.com>

opendevin/server/agent/agent.py

@@ -184,7 +184,8 @@ class AgentUnit:
             await self.send_error('No agent started. Please wait a second...')
             return
         try:
-            assert not self.agent_task, 'Agent task already running'
+            if self.agent_task:
+                self.agent_task.cancel()
             self.agent_task = asyncio.create_task(
                 self.controller.start(task), name='agent start task loop'
             )