patch 8.2.4131: Vim9: calling function in autoload import does not work

Problem:    Vim9: calling function in autoload import does not work in a :def
            function.
Solution:   When a variable is not found and a PCALL follows use a funcref.
            (closes #9550)
diff --git a/src/testdir/test_vim9_import.vim b/src/testdir/test_vim9_import.vim
index 1378261..1353015 100644
--- a/src/testdir/test_vim9_import.vim
+++ b/src/testdir/test_vim9_import.vim
@@ -1264,6 +1264,10 @@
   var lines =<< trim END
      vim9script autoload
 
+     export def RetArg(arg: string): string
+       return arg
+     enddef
+
      export def Getother()
        g:result = 'other'
      enddef
@@ -1273,6 +1277,13 @@
   lines =<< trim END
       vim9script
       import autoload 'another.vim'
+
+      # compile this before 'another.vim' is loaded
+      def CallAnother()
+        assert_equal('foo', 'foo'->another.RetArg())
+      enddef
+      CallAnother()
+
       call another.Getother()
       assert_equal('other', g:result)
   END