Fix deadlock in ICEAgent, early exit failed to unlock mutex

Reported+Fixed by @backkem

pkg/ice/agent.go

@@ -146,6 +146,7 @@ func (a *Agent) agentTaskLoop() {
 			a.Lock()
 			if a.isControlling {
 				if assertSelectedPairValid() {
+					a.Unlock()
 					continue
 				}