patch 8.2.0358: insufficient testing for indent.c

Problem:    Insufficient testing for indent.c.
Solution:   Add indent tests. (Yegappan Lakshmanan, closes #5736)
diff --git a/src/testdir/test_lispwords.vim b/src/testdir/test_lispwords.vim
index aa5a738..ff710b2 100644
--- a/src/testdir/test_lispwords.vim
+++ b/src/testdir/test_lispwords.vim
@@ -45,6 +45,7 @@
 	      \ ])
   call assert_equal(7, lispindent(2))
   call assert_equal(5, 6->lispindent())
+  call assert_equal(-1, lispindent(-1))
 
   set lisp
   set lispwords&
@@ -83,3 +84,5 @@
   let &cpoptions=save_copt
   set nolisp
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab