patch 8.0.1193: crash when wiping out a buffer after using getbufinfo()

Problem:    Crash when wiping out a buffer after using getbufinfo().
            (Yegappan Lakshmanan)
Solution:   Remove b:changedtick from the buffer variables.

src/buffer.c

@@ -837,6 +837,8 @@ free_buffer(buf_T *buf)
     ++buf_free_count;
     free_buffer_stuff(buf, TRUE);
 #ifdef FEAT_EVAL
+    /* b:changedtick uses an item in buf_T, remove it now */
+    dictitem_remove(buf->b_vars, (dictitem_T *)&buf->b_ct_di);
     unref_var_dict(buf->b_vars);
 #endif
 #ifdef FEAT_LUA

src/testdir/test_autocmd.vim

@@ -769,10 +769,14 @@ func Test_BufLeave_Wipe()
   bwipe!
   call assert_equal(1, line('$'))
   call assert_equal('', bufname('%'))
-  call assert_equal(1, len(getbufinfo()))
+  let g:bufinfo = getbufinfo()
+  call assert_equal(1, len(g:bufinfo))
 
   call delete('Xxx1')
   call delete('Xxx2')
   %bwipe
   au! BufLeave
+
+  " check that bufinfo doesn't contain a pointer to freed memory
+  call test_garbagecollect_now()
 endfunc

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1193,
 /**/
     1192,
 /**/