patch 8.0.0681: unnamed register only contains the last deleted text

Problem:    Unnamed register only contains the last deleted text when
            appending deleted text to a register. (Wolfgang Jeltsch)
Solution:   Only set y_previous when not using y_append. (Christian Brabandt)
diff --git a/src/testdir/test_put.vim b/src/testdir/test_put.vim
index 38c812b..18c7f4e 100644
--- a/src/testdir/test_put.vim
+++ b/src/testdir/test_put.vim
@@ -34,3 +34,14 @@
   bw!
   call setreg('a', a[0], a[1])
 endfunc
+
+func Test_put_lines()
+  new
+  let a = [ getreg('a'), getregtype('a') ]
+  call setline(1, ['Line 1', 'Line2', 'Line 3', ''])
+  exe 'norm! gg"add"AddG""p'
+  call assert_equal(['Line 3', '', 'Line 1', 'Line2'], getline(1,'$'))
+  " clean up
+  bw!
+  call setreg('a', a[0], a[1])
+endfunc