race condition: ast_dial_join() may not cancel outgoing call, if
function is called just after called party answer and before
application execution (bit is_running_app not yet set).

This fix adds ast_softhangup() calls in addition to existing
pthread_kill() when is_running_app is not set.

ASTERISK-30258

Change-Id: Idbdd5c15122159661aa8e996a42d5800083131e4