patch 9.1.1317: noisy error when restoring folds from session fails

Problem:  noisy error when restoring folds from session fails
Solution: ignore errors silently when sourcing session file.
          (Igor Lacerda)

fixes: #15813
closes: #17127

Signed-off-by: Igor Lacerda <igorlfs@ufmg.br>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_mksession.vim b/src/testdir/test_mksession.vim
index d0ee6e8..72a9376 100644
--- a/src/testdir/test_mksession.vim
+++ b/src/testdir/test_mksession.vim
@@ -1264,6 +1264,24 @@
   bw!
 endfunc
 
+" Test for handling invalid folds within views
+func Test_mkview_ignore_invalid_folds()
+  call writefile(range(1,10), 'Xmkvfile', 'D')
+  new Xmkvfile
+  " create some folds
+  5,6fold
+  4,7fold
+  mkview Xview
+  normal zE
+  " delete lines to make folds invalid
+  call deletebufline('', 6, '$')
+  source Xview
+  call assert_equal([-1, -1, -1, -1, -1, -1], [foldclosed(3), foldclosed(4),
+        \ foldclosed(5), foldclosed(6), foldclosed(7), foldclosed(8)])
+  call delete('Xview')
+  bw!
+endfunc
+
 " Test default 'viewdir' value
 func Test_mkview_default_home()
   if has('win32')