patch 8.0.1475: invalid memory access in read_redo()

Problem:    Invalid memory access in read_redo(). (gy741)
Solution:   Convert the replacement character back from a negative number to
            CR or NL. (hint by Dominique Pelle, closes #2616)
diff --git a/src/testdir/test_undo.vim b/src/testdir/test_undo.vim
index cc3cceb..c1b821e 100644
--- a/src/testdir/test_undo.vim
+++ b/src/testdir/test_undo.vim
@@ -403,3 +403,10 @@
 
   bwipe!
 endfunc
+
+func Test_redo_empty_line()
+  new
+  exe "norm\x16r\x160"
+  exe "norm."
+  bwipe!
+endfunc