patch 8.2.4953: with 'si' inserting '}' after completion goes wrong

Problem:    With 'smartindent' inserting '}' after completion goes wrong.
Solution:   Check the cursor is in indent.  (closes #10420)

src/testdir/test_smartindent.vim

@@ -140,6 +140,11 @@ func Test_si_after_completion()
   call setline(1, 'foo foot')
   call feedkeys("o  f\<C-X>\<C-N>#", 'tx')
   call assert_equal('  foo#', getline(2))
+
+  call setline(2, '')
+  call feedkeys("1Go  f\<C-X>\<C-N>}", 'tx')
+  call assert_equal('  foo}', getline(2))
+
   bwipe!
 endfunc