patch 8.2.1004: line numbers below filler lines not always updated

Problem:    Line numbers below filler lines not always updated.
Solution:   Don't break out of the win_line() loop too early. (Christian
            Brabandt, closes #6294, closes #6138)
diff --git a/src/testdir/test_diffmode.vim b/src/testdir/test_diffmode.vim
index a251d3f..4544834 100644
--- a/src/testdir/test_diffmode.vim
+++ b/src/testdir/test_diffmode.vim
@@ -1093,4 +1093,29 @@
   %bwipe!
 endfunc
 
+func Test_diff_rnu()
+  CheckScreendump
+
+  let content =<< trim END
+    call setline(1, ['a', 'a', 'a', 'y', 'b', 'b', 'b', 'b', 'b'])
+    vnew
+    call setline(1, ['a', 'a', 'a', 'x', 'x', 'x', 'b', 'b', 'b', 'b', 'b'])
+    windo diffthis
+    setlocal number rnu foldcolumn=0
+  END
+  call writefile(content, 'Xtest_diff_rnu')
+  let buf = RunVimInTerminal('-S Xtest_diff_rnu', {})
+
+  call VerifyScreenDump(buf, 'Test_diff_rnu_01', {})
+
+  call term_sendkeys(buf, "j")
+  call VerifyScreenDump(buf, 'Test_diff_rnu_02', {})
+  call term_sendkeys(buf, "j")
+  call VerifyScreenDump(buf, 'Test_diff_rnu_03', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('Xtest_diff_rnu')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab