patch 7.4.1828
Problem:    May try to access buffer that's already freed.
Solution:   When freeing a buffer remove it from any channel.
diff --git a/src/proto/channel.pro b/src/proto/channel.pro
index 5e0bec5..5dc5121 100644
--- a/src/proto/channel.pro
+++ b/src/proto/channel.pro
@@ -14,6 +14,7 @@
 void channel_set_job(channel_T *channel, job_T *job, jobopt_T *options);
 void channel_set_options(channel_T *channel, jobopt_T *opt);
 void channel_set_req_callback(channel_T *channel, int part, char_u *callback, partial_T *partial, int id);
+void channel_buffer_free(buf_T *buf);
 void channel_write_any_lines(void);
 void channel_write_new_lines(buf_T *buf);
 char_u *channel_get(channel_T *channel, int part);