patch 8.2.4275: cannot use an autoload function from a package under start

Problem:    Cannot use an autoload function from a package under start.
Solution:   Also look in the "start" package directory. (Bjorn Linse,
            closes #7193)
diff --git a/src/testdir/test_packadd.vim b/src/testdir/test_packadd.vim
index d7a38da..8ca9b41 100644
--- a/src/testdir/test_packadd.vim
+++ b/src/testdir/test_packadd.vim
@@ -246,6 +246,19 @@
   call assert_equal(4321, g:plugin_bar_number)
 endfunc
 
+func Test_start_autoload()
+  " plugin foo with an autoload directory
+  let autodir = &packpath .. '/pack/mine/start/foo/autoload'
+  call mkdir(autodir, 'p')
+  let fname = autodir .. '/foobar.vim'
+  call writefile(['func foobar#test()',
+	\ '  return 1666',
+	\ 'endfunc'], fname)
+
+  call assert_equal(1666, foobar#test())
+  call delete(fname)
+endfunc
+
 func Test_helptags()
   let docdir1 = &packpath . '/pack/mine/start/foo/doc'
   let docdir2 = &packpath . '/pack/mine/start/bar/doc'