patch 8.2.3612: using freed memory with regexp using a mark

Problem:    Using freed memory with regexp using a mark.
Solution:   Get the line again after getting the mark position.
diff --git a/src/testdir/test_regexp_latin.vim b/src/testdir/test_regexp_latin.vim
index c487b27..96c3177 100644
--- a/src/testdir/test_regexp_latin.vim
+++ b/src/testdir/test_regexp_latin.vim
@@ -1037,4 +1037,12 @@
   set re&
 endfunc
 
+func Test_using_mark_position()
+  " this was using freed memory
+  new
+  norm O0
+  call assert_fails("s/\\%')", 'E486:')
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab