patch 8.2.0644: insufficient testing for invalid function arguments

Problem:    Insufficient testing for invalid function arguments.
Solution:   Add more tests. (Yegappan Lakshmanan, closes #5988)

src/testdir/test_expr.vim

@@ -471,6 +471,7 @@ func Test_setmatches()
   endif
   eval set->setmatches()
   call assert_equal(exp, getmatches())
+  call assert_fails('let m = setmatches([], [])', 'E957:')
 endfunc
 
 func Test_empty_concatenate()