vim-patch:8.0.1202: :wall gives an errof for a terminal window

Problem:    :wall gives an errof for a terminal window. (Marius Gedminas)
Solution:   Don't try writing a buffer that can't be written. (Yasuhiro
            Matsumoto, closes vim/vim#2190)
059db5c29f

src/nvim/ex_cmds.c

@@ -1939,7 +1939,7 @@ void do_wqall(exarg_T *eap)
   }
 
   FOR_ALL_BUFFERS(buf) {
-    if (!bufIsChanged(buf)) {
+    if (!bufIsChanged(buf) || bt_dontwrite(buf)) {
       continue;
     }
     /*