patch 8.2.3949: using freed memory with /\%V

Problem:    Using freed memory with /\%V.
Solution:   Get the line again after getvvcol().

src/regexp.c

@@ -1310,9 +1310,9 @@ reg_match_visual(void)
     if (lnum < top.lnum || lnum > bot.lnum)
 	return FALSE;
 
+    col = (colnr_T)(rex.input - rex.line);
     if (mode == 'v')
     {
-	col = (colnr_T)(rex.input - rex.line);
 	if ((lnum == top.lnum && col < top.col)
 		|| (lnum == bot.lnum && col >= bot.col + (*p_sel != 'e')))
 	    return FALSE;
@@ -1327,7 +1327,12 @@ reg_match_visual(void)
 	    end = end2;
 	if (top.col == MAXCOL || bot.col == MAXCOL || curswant == MAXCOL)
 	    end = MAXCOL;
-	cols = win_linetabsize(wp, rex.line, (colnr_T)(rex.input - rex.line));
+
+	// getvvcol() flushes rex.line, need to get it again
+	rex.line = reg_getline(rex.lnum);
+	rex.input = rex.line + col;
+
+	cols = win_linetabsize(wp, rex.line, col);
 	if (cols < start || cols > end - (*p_sel == 'e'))
 	    return FALSE;
     }

src/testdir/test_regexp_latin.vim

@@ -1045,4 +1045,12 @@ func Test_using_mark_position()
   bwipe!
 endfunc
 
+func Test_using_visual_position()
+  " this was using freed memory
+  new
+  exe "norm 0o\<Esc>\<C-V>k\<C-X>o0"
+  /\%V
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3949,
 /**/
     3948,
 /**/