vim-patch:8.1.1360: buffer left 'nomodifiable' after :substitute

Problem:    Buffer left 'nomodifiable' after :substitute. (Ingo Karkat)
Solution:   Save the value of 'modifiable' earlier' (Christian Brabandt,
            closes vim/vim#4403)
80341bcd89

src/nvim/ex_cmds.c

@@ -3817,6 +3817,7 @@ static buf_T *do_sub(exarg_T *eap, proftime_T timeout,
         // 3. Substitute the string. During 'inccommand' preview only do this if
         //    there is a replace pattern.
         if (!preview || has_second_delim) {
+          save_ma = curbuf->b_p_ma;
           if (subflags.do_count) {
             // prevent accidentally changing the buffer by a function
             curbuf->b_p_ma = false;

src/nvim/testdir/test_substitute.vim

@@ -612,9 +612,24 @@ func Test_sub_replace_10()
    call assert_equal('1aaa', substitute('123', '1\zs\|[23]', 'a', 'g'))
 endfunc
 
+func Test_sub_cmd_9()
+  new
+  let input = ['1 aaa', '2 aaa', '3 aaa']
+  call setline(1, input)
+  func Foo()
+    return submatch(0)
+  endfunc
+  %s/aaa/\=Foo()/gn
+  call assert_equal(input, getline(1, '$'))
+  call assert_equal(1, &modifiable)
+
+  delfunc Foo
+  bw!
+endfunc
+
 func Test_nocatch_sub_failure_handling()
   " normal error results in all replacements 
-  func! Foo()
+  func Foo()
     foobar
   endfunc
   new
@@ -650,6 +665,7 @@ func Test_nocatch_sub_failure_handling()
   call assert_equal(1, error_caught)
   call assert_equal(['1 aaa', '2 aaa', '3 aaa'], getline(1, 3))
 
+  delfunc Foo
   bwipe!
 endfunc