vim-patch:8.1.2349: :lockvar and :unlockvar cannot be followed by "| endif"

Problem:    :lockvar and :unlockvar cannot be followed by "| endif".
Solution:   Check for following commands. (closes vim/vim#5269)
cc4423ae13

src/nvim/ex_docmd.c

@@ -2151,6 +2151,7 @@ static char_u * do_one_cmd(char_u **cmdlinep,
     case CMD_leftabove:
     case CMD_let:
     case CMD_lockmarks:
+    case CMD_lockvar:
     case CMD_lua:
     case CMD_match:
     case CMD_mzscheme:
@@ -2179,6 +2180,7 @@ static char_u * do_one_cmd(char_u **cmdlinep,
     case CMD_tilde:
     case CMD_topleft:
     case CMD_unlet:
+    case CMD_unlockvar:
     case CMD_verbose:
     case CMD_vertical:
     case CMD_wincmd:

src/nvim/testdir/test_const.vim

@@ -182,6 +182,20 @@ func Test_const_with_condition()
   call assert_equal(0, x)
 endfunc
 
+func Test_lockvar()
+  let x = 'hello'
+  lockvar x
+  call assert_fails('let x = "there"', 'E741')
+  if 0 | unlockvar x | endif
+  call assert_fails('let x = "there"', 'E741')
+  unlockvar x
+  let x = 'there'
+
+  if 0 | lockvar x | endif
+  let x = 'again'
+endfunc
+
+
 func Test_const_with_index_access()
     let l = [1, 2, 3]
     call assert_fails('const l[0] = 4', 'E996:')