patch 8.1.1606: on a narrow screen ":hi" output is confusing

Problem:    On a narrow screen ":hi" output is confusing.
Solution:   Insert a space between highlight group name and "xxx". (Masato
            Nishihaga, closes #4599)

src/syntax.c

@@ -9440,6 +9440,7 @@ syn_list_header(
 {
     int	    endcol = 19;
     int	    newline = TRUE;
+    int	    name_col = 0;
 
     if (!did_header)
     {
@@ -9447,6 +9448,7 @@ syn_list_header(
 	if (got_int)
 	    return TRUE;
 	msg_outtrans(HL_TABLE()[id - 1].sg_name);
+	name_col = msg_col;
 	endcol = 15;
     }
     else if (msg_col + outlen + 1 >= Columns)
@@ -9471,6 +9473,8 @@ syn_list_header(
     /* Show "xxx" with the attributes. */
     if (!did_header)
     {
+	if (endcol == Columns - 1 && endcol <= name_col)
+	    msg_putchar(' ');
 	msg_puts_attr("xxx", syn_id2attr(id));
 	msg_putchar(' ');
     }

src/testdir/test_highlight.vim

@@ -607,3 +607,11 @@ func Test_1_highlight_Normalgroup_exists()
     call assert_match('hi Normal\s*clear', hlNormal)
   endif
 endfunc
+
+function Test_no_space_before_xxx()
+  let l:org_columns = &columns
+  set columns=17
+  let l:hi_StatusLineTermNC = join(split(execute('hi StatusLineTermNC')))
+  call assert_match('StatusLineTermNC xxx', l:hi_StatusLineTermNC)
+  let &columns = l:org_columns
+endfunction

src/version.c

@@ -777,6 +777,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1606,
 /**/
     1605,
 /**/