patch 9.0.1606: using freed memory when 'foldcolumn' is set

Problem:    Using freed memory when 'foldcolumn' is set.
Solution:   Save extra pointer to free it later. (closes #12492)

src/testdir/test_fold.vim

@@ -1755,4 +1755,18 @@ func Test_fold_screenrow_motion()
   norm Ggkzo
   call assert_equal(1, line('.'))
 endfunc
+
+" This was using freed memory
+func Test_foldcolumn_linebreak_control_char()
+  CheckFeature linebreak
+
+  5vnew
+  setlocal foldcolumn=1 linebreak
+  call setline(1, "aaa\<C-A>b")
+  redraw
+  call assert_equal([' aaa^', ' Ab  '], ScreenLines([1, 2], 5))
+  call assert_equal(screenattr(1, 5), screenattr(2, 2))
+
+  bwipe!
+endfunc