Fix a race condition while adding a source, that causes the notify callback to be called before the end of belle_sip_main_loop_add_source() if the timeout is set to 0.
(cherry picked from commit 36d95d86)
Fix a race condition while adding a source, that causes the notify callback to be called before the end of belle_sip_main_loop_add_source() if the timeout is set to 0.
(cherry picked from commit 36d95d86)