stasis: Call callbacks when imparting fails

After a bridge has been deleted the stasis control will depart
the channel and might attempt to re-add it to the dial bridge.

The later can fail and this can lead to a situation that the stasis
control is unlinked but the after_bridge_cb_failed cb is executed trying
to access a dangling control object.

Fix it by calling the after_cb's before bridge_channel_impart_signal.

ASTERISK-26718

Change-Id: Ib4e8f70d7a21bd54afe3cb51cc6717ef7c355496

main/bridge.c

@@ -1953,6 +1953,7 @@ int ast_bridge_impart(struct ast_bridge *bridge,
 	res = bridge_impart_internal(bridge, chan, swap, features, flags, &cond);
 	if (res) {
 		/* Impart failed.  Signal any other waiting impart threads */
+		ast_bridge_discard_after_callback(chan, AST_BRIDGE_AFTER_CB_REASON_IMPART_FAILED);
 		bridge_channel_impart_signal(chan);
 	}