patch 8.2.4091: virtcol is recomputed for statusline unnecessarily

Problem:    Virtcol is recomputed for statusline unnecessarily.
Solution:   Just use "w_virtcol". (closes #9523)

src/buffer.c

@@ -4610,15 +4610,7 @@ build_stl_str_hl(
 
 	case STL_VIRTCOL:
 	case STL_VIRTCOL_ALT:
-	    // In list mode virtcol needs to be recomputed
+	    virtcol = wp->w_virtcol + 1;
-	    virtcol = wp->w_virtcol;
-	    if (wp->w_p_list && wp->w_lcs_chars.tab1 == NUL)
-	    {
-		wp->w_p_list = FALSE;
-		getvcol(wp, &wp->w_cursor, NULL, &virtcol, NULL);
-		wp->w_p_list = TRUE;
-	    }
-	    ++virtcol;
 	    // Don't display %V if it's the same as %c.
 	    if (opt == STL_VIRTCOL_ALT
 		    && (virtcol == (colnr_T)(!(State & INSERT) && empty_line

src/testdir/test_statusline.vim

@@ -196,7 +196,16 @@ func Test_statusline()
   set virtualedit=all
   norm 10|
   call assert_match('^10,-10\s*$', s:get_statusline())
+  set list
+  call assert_match('^10,-10\s*$', s:get_statusline())
   set virtualedit&
+  exe "norm A\<Tab>\<Tab>a\<Esc>"
+  " In list mode a <Tab> is shown as "^I", which is 2-wide.
+  call assert_match('^9,-9\s*$', s:get_statusline())
+  set list&
+  " Now the second <Tab> ends at the 16th screen column.
+  call assert_match('^17,-17\s*$', s:get_statusline())
+  undo
 
   " %w: Preview window flag, text is "[Preview]".
   " %W: Preview window flag, text is ",PRV".

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4091,
 /**/
     4090,
 /**/