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/buffer.c b/src/buffer.c
index 9bc24bc..e884f55 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -676,6 +676,9 @@
 #ifdef FEAT_RUBY
     ruby_buffer_free(buf);
 #endif
+#ifdef FEAT_JOB_CHANNEL
+    channel_buffer_free(buf);
+#endif
 #ifdef FEAT_AUTOCMD
     aubuflocal_remove(buf);
     if (autocmd_busy)