vim-patch:8.0.0998: strange error when using K while only spaces are selected

Problem:    Strange error when using K while only spaces are selected.
            (Christian J. Robinson)
Solution:   Check for blank argument.
a4f99f5a8b

src/nvim/normal.c

@@ -4771,6 +4771,10 @@ static void nv_ident(cmdarg_T *cap)
   assert(*kp != NUL);  // option.c:do_set() should default to ":help" if empty.
   bool kp_ex = (*kp == ':');  // 'keywordprg' is an ex command
   bool kp_help = (STRCMP(kp, ":he") == 0 || STRCMP(kp, ":help") == 0);
+  if (kp_help && *skipwhite(ptr) == NUL) {
+    EMSG(_(e_noident));   // found white space only
+    return;
+  }
   size_t buf_size = n * 2 + 30 + STRLEN(kp);
   char *buf = xmalloc(buf_size);
   buf[0] = NUL;

src/nvim/testdir/test_help.vim

@@ -13,4 +13,21 @@ endfunc
 func Test_help_errors()
   call assert_fails('help doesnotexist', 'E149:')
   call assert_fails('help!', 'E478:')
+
+  new
+  set keywordprg=:help
+  call setline(1, "   ")
+  call assert_fails('normal VK', 'E349:')
+  bwipe!
+endfunc
+
+func Test_help_keyword()
+  new
+  set keywordprg=:help
+  call setline(1, "  Visual ")
+  normal VK
+  call assert_match('^Visual mode', getline('.'))
+  call assert_equal('help', &ft)
+  close
+  bwipe!
 endfunc