patch 8.1.0449: when 'rnu' is set folded lines are not displayed correctly

Problem:    When 'rnu' is set folded lines are not displayed correctly.
            (Vitaly Yashin)
Solution:   When only redrawing line numbers do draw folded lines.
            (closes #3484)
diff --git a/src/testdir/dumps/Test_folds_with_rnu_01.dump b/src/testdir/dumps/Test_folds_with_rnu_01.dump
new file mode 100644
index 0000000..15a44d1
--- /dev/null
+++ b/src/testdir/dumps/Test_folds_with_rnu_01.dump
@@ -0,0 +1,20 @@
+|++0#0000e05#a8a8a8255| @2|0| >+|-@1| @1|2| |l|i|n|e|s|:| |-@54
+|+| @2|1| |+|-@1| @1|2| |l|i|n|e|s|:| |-@54
+| @1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000000&@56|1|,|1| @10|A|l@1| 
diff --git a/src/testdir/dumps/Test_folds_with_rnu_02.dump b/src/testdir/dumps/Test_folds_with_rnu_02.dump
new file mode 100644
index 0000000..60d4eb3
--- /dev/null
+++ b/src/testdir/dumps/Test_folds_with_rnu_02.dump
@@ -0,0 +1,20 @@
+|++0#0000e05#a8a8a8255| @2|1| |+|-@1| @1|2| |l|i|n|e|s|:| |-@54
+|+| @2|0| >+|-@1| @1|2| |l|i|n|e|s|:| |-@54
+| @1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000e05#a8a8a8255@1|~+0#4040ff13#ffffff0| @71
+| +0#0000000&@56|3|,|1| @10|A|l@1| 
diff --git a/src/testdir/test_fold.vim b/src/testdir/test_fold.vim
index df4b12c..0384b4f 100644
--- a/src/testdir/test_fold.vim
+++ b/src/testdir/test_fold.vim
@@ -1,6 +1,7 @@
 " Test for folding
 
 source view_util.vim
+source screendump.vim
 
 func PrepIndent(arg)
   return [a:arg] + repeat(["\t".a:arg], 5)
@@ -674,3 +675,23 @@
   set fdm&
   enew!
 endfunc
+
+func Test_folds_with_rnu()
+  if !CanRunVimInTerminal()
+    return
+  endif
+
+  call writefile([
+	\ 'set fdm=marker rnu foldcolumn=2',
+	\ 'call setline(1, ["{{{1", "nline 1", "{{{1", "line 2"])',
+	\ ], 'Xtest_folds_with_rnu')
+  let buf = RunVimInTerminal('-S Xtest_folds_with_rnu', {})
+
+  call VerifyScreenDump(buf, 'Test_folds_with_rnu_01', {})
+  call term_sendkeys(buf, "j")
+  call VerifyScreenDump(buf, 'Test_folds_with_rnu_02', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('Xtest_folds_with_rnu')
+endfunc