Fix nil pointer exception when load empty list and try to cast it (#3282)

client/internal/peer/ice/config.go

@@ -1,14 +1,12 @@
 package ice
 
 import (
-	"sync/atomic"
-
 	"github.com/pion/ice/v3"
 )
 
 type Config struct {
 	// StunTurn is a list of STUN and TURN URLs
-	StunTurn *atomic.Value // []*stun.URI
+	StunTurn *StunTurn // []*stun.URI
 
 	// InterfaceBlackList is a list of machine interfaces that should be filtered out by ICE Candidate gathering
 	// (e.g. if eth0 is in the list, host candidate of this interface won't be used)