vim-patch:8.1.0043: ++bad argument of :edit does not work properly

Problem:    ++bad argument of :edit does not work properly.
Solution:   Return FAIL from get_bad_opt() only when there is no valid
            argument. (Dominique Pelle, Christian Brabandt, closes vim/vim#2966,
            closes vim/vim#2947)
7580849df9

src/nvim/ex_docmd.c

@@ -4547,8 +4547,10 @@ int get_bad_opt(const char_u *p, exarg_T *eap)
     eap->bad_char = BAD_DROP;
   } else if (MB_BYTE2LEN(*p) == 1 && p[1] == NUL) {
     eap->bad_char = *p;
+  } else {
+    return FAIL;
   }
-  return FAIL;
+  return OK;
 }
 
 /*

src/nvim/testdir/test_plus_arg_edit.vim

@@ -8,3 +8,31 @@ function Test_edit()
   call delete('Xfile1')
   call delete('Xfile2')
 endfunction
+
+func Test_edit_bad()
+  if !has('multi_byte')
+    finish
+  endif
+
+  " Test loading a utf8 file with bad utf8 sequences.
+  call writefile(["[\xff][\xc0][\xe2\x89\xf0][\xc2\xc2]"], "Xfile")
+  new
+
+  " Without ++bad=..., the default behavior is like ++bad=?
+  e! ++enc=utf8 Xfile
+  call assert_equal('[?][?][???][??]', getline(1))
+
+  e! ++enc=utf8 ++bad=_ Xfile
+  call assert_equal('[_][_][___][__]', getline(1))
+
+  e! ++enc=utf8 ++bad=drop Xfile
+  call assert_equal('[][][][]', getline(1))
+
+  e! ++enc=utf8 ++bad=keep Xfile
+  call assert_equal("[\xff][\xc0][\xe2\x89\xf0][\xc2\xc2]", getline(1))
+
+  call assert_fails('e! ++enc=utf8 ++bad=foo Xfile', 'E474:')
+
+  bw!
+  call delete('Xfile')
+endfunc