patch 8.1.2282: crash when passing many arguments through a partial

Problem:    Crash when passing many arguments through a partial. (Andy
            Massimino)
Solution:   Check the number of arguments. (closes #5186)
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index 253cd49..eb51cd6 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -496,6 +496,8 @@
   let OneByRef = 'One'->funcref()
   call assert_equal(2, OneByRef())
   call assert_fails('echo funcref("{")', 'E475:')
+  let OneByRef = funcref("One", repeat(["foo"], 20))
+  call assert_fails('let OneByRef = funcref("One", repeat(["foo"], 21))', 'E118:')
 endfunc
 
 func Test_setmatches()
diff --git a/src/testdir/test_substitute.vim b/src/testdir/test_substitute.vim
index b30464f..c7532fb 100644
--- a/src/testdir/test_substitute.vim
+++ b/src/testdir/test_substitute.vim
@@ -408,9 +408,20 @@
 func SubReplacer(text, submatches)
   return a:text .. a:submatches[0] .. a:text
 endfunc
+func SubReplacer20(t1, t2, t3, t4, t5, t6, t7, t8, t9, t10, t11, t12, t13, t14, t15, t16, t17, t18, t19, submatches)
+  return a:t3 .. a:submatches[0] .. a:t11
+endfunc
 
 func Test_substitute_partial()
    call assert_equal('1foo2foo3', substitute('123', '2', function('SubReplacer', ['foo']), 'g'))
+
+   " 19 arguments plus one is just OK
+   let Replacer = function('SubReplacer20', repeat(['foo'], 19))
+   call assert_equal('1foo2foo3', substitute('123', '2', Replacer, 'g'))
+
+   " 20 arguments plus one is too many
+   let Replacer = function('SubReplacer20', repeat(['foo'], 20))
+   call assert_fails("call substitute('123', '2', Replacer, 'g')", 'E118')
 endfunc
 
 " Tests for *sub-replace-special* and *sub-replace-expression* on :substitute.