patch 8.2.1936: session sets the local 'scrolloff' value to the global value

Problem:    Session sets the local 'scrolloff' value to the global value.
Solution:   Do not let restoring the global option value change the local
            value.
diff --git a/src/testdir/test_mksession.vim b/src/testdir/test_mksession.vim
index 06be838..7ae42f3 100644
--- a/src/testdir/test_mksession.vim
+++ b/src/testdir/test_mksession.vim
@@ -859,4 +859,17 @@
   call delete('Xtestvimrc')
 endfunc
 
+func Test_scrolloff()
+  set sessionoptions+=localoptions
+  setlocal so=1 siso=1
+  mksession! Xtest_mks.out
+  setlocal so=-1 siso=-1
+  source Xtest_mks.out
+  call assert_equal(1, &l:so)
+  call assert_equal(1, &l:siso)
+  call delete('Xtest_mks.out')
+  setlocal so& siso&
+  set sessionoptions&
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab