patch 8.2.0270: some code not covered by tests

Problem:    Some code not covered by tests.
Solution:   Add test cases. (Yegappan Lakshmanan, closes #5649)
diff --git a/src/testdir/test_move.vim b/src/testdir/test_move.vim
index f666a90..8c40369 100644
--- a/src/testdir/test_move.vim
+++ b/src/testdir/test_move.vim
@@ -38,6 +38,7 @@
   call assert_fails("move -100", 'E16:')
   call assert_fails("move +100", 'E16:')
   call assert_fails('move', 'E16:')
+  call assert_fails("move 'r", 'E20:')
 
   %bwipeout!
 endfunc