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)

src/scriptfile.c

@@ -2294,7 +2294,7 @@ script_autoload(
 
 	// Try loading the package from $VIMRUNTIME/autoload/<name>.vim
 	// Use "ret_sid" to avoid loading the same script again.
-	if (source_in_path(p_rtp, scriptname, 0, &ret_sid) == OK)
+	if (source_in_path(p_rtp, scriptname, DIP_START, &ret_sid) == OK)
 	    ret = TRUE;
     }
 

src/testdir/test_packadd.vim

@@ -246,6 +246,19 @@ func Test_packloadall()
   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'

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4275,
 /**/
     4274,
 /**/