patch 8.1.0022: repeating put from expression register fails

Problem:    Repeating put from expression register fails.
Solution:   Re-evaluate the expression register. (Andy Massimino,
            closes #2945)
diff --git a/src/testdir/test_put.vim b/src/testdir/test_put.vim
index 18c7f4e..0a23a43 100644
--- a/src/testdir/test_put.vim
+++ b/src/testdir/test_put.vim
@@ -45,3 +45,16 @@
   bw!
   call setreg('a', a[0], a[1])
 endfunc
+
+func Test_put_expr()
+  new
+  call setline(1, repeat(['A'], 6))
+  exec "1norm! \"=line('.')\<cr>p"
+  norm! j0.
+  norm! j0.
+  exec "4norm! \"=\<cr>P"
+  norm! j0.
+  norm! j0.
+  call assert_equal(['A1','A2','A3','4A','5A','6A'], getline(1,'$'))
+  bw!
+endfunc