patch 8.1.1681: insert stray "{" when listener gets buffer line

Problem:    Insert stray "{" when listener gets buffer line. (Paul Jolly)
Solution:   Flush the cached line after invoking listeners. (closes #4455)

src/memline.c

@@ -2836,8 +2836,10 @@ ml_append_int(
 
 #ifdef FEAT_EVAL
     // When inserting above recorded changes: flush the changes before changing
-    // the text.
+    // the text.  Then flush the cached line, it may become invalid.
     may_invoke_listeners(buf, lnum + 1, lnum + 1, 1);
+    if (curbuf->b_ml.ml_line_lnum != 0)
+	ml_flush_line(curbuf);
 #endif
 
 #ifdef FEAT_TEXT_PROP

src/testdir/test_listener.vim

@@ -242,3 +242,29 @@ func Test_listener_garbage_collect()
   delfunc MyListener
   bwipe!
 endfunc
+
+" This verifies the fix for issue #4455
+func Test_listener_caches_buffer_line()
+  new
+  inoremap <silent> <CR> <CR><Esc>O
+
+  function EchoChanges(bufnr, start, end, added, changes)
+    for l:change in a:changes
+      let text = getbufline(a:bufnr, l:change.lnum, l:change.end-1+l:change.added)
+    endfor
+  endfunction
+  let lid = listener_add("EchoChanges")
+  set autoindent
+  set cindent
+
+  call setline(1, ["{", "\tif true {}", "}"])
+  exe "normal /{}\nl"
+  call feedkeys("i\r\e", 'xt')
+  call assert_equal(["{", "\tif true {", "", "\t}", "}"], getline(1, 5))
+
+  bwipe!
+  delfunc EchoChanges
+  call listener_remove(lid)
+  iunmap <CR>
+  set nocindent
+endfunc

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1681,
 /**/
     1680,
 /**/