Fix "REFER declined" deadlock

This occurs when the user declines an incoming call transfer request,
due to the following path:

- recvd_refer_permission() acquires a read lock over lines_mtx
- move_releasing_lines_to_background() is called
- A write lock over lines_mtx is acquired

1 files changed, 1 insertions, 1 deletions

diff --git a/src/phone.cpp b/src/phone.cpp
index 401abb1..2718c82 100644
--- a/src/phone.cpp
+++ b/src/phone.cpp
@@ -1871,7 +1871,7 @@ void t_phone::recvd_refer_permission(bool permission) {
 	t_phone_user *pu = incoming_refer_data->get_phone_user();
 	t_user *user_config = pu->get_user_profile();
 			
-	t_rwmutex_reader x(lines_mtx);
+	t_rwmutex_future_writer x(lines_mtx);
 	lines[i]->recvd_refer_permission(permission, r);
 	
 	if (!permission) {