mavlink: COLLISION stream check free tx buf before send

src/modules/mavlink/streams/COLLISION.hpp

@@ -85,7 +85,7 @@ protected:
 		collision_report_s report;
 		bool sent = false;
 
-		while (_collision_sub.update(&report)) {
+		while ((_mavlink->get_free_tx_buf() >= get_size()) && _collision_sub.update(&report)) {
 			mavlink_collision_t msg = {};
 
 			msg.src = report.src;