patch 8.2.2600: Vim9: crash when putting an unknown type in a dictionary

Problem:    Vim9: crash when putting an unknown type in a dictionary.
            (Yegappan Lakshmanan)
Solution:   Handle a NULL type pointer.
diff --git a/src/testdir/test_vim9_builtin.vim b/src/testdir/test_vim9_builtin.vim
index 8ec3db1..75bbc0c 100644
--- a/src/testdir/test_vim9_builtin.vim
+++ b/src/testdir/test_vim9_builtin.vim
@@ -340,6 +340,26 @@
   CheckScriptFailure(['vim9script'] + lines, 'E1012:', 1)
 enddef
 
+def Test_extend_with_error_function()
+  var lines =<< trim END
+      vim9script
+      def F()
+        {
+          var m = 10
+        }
+        echo m
+      enddef
+
+      def Test()
+        var d: dict<any> = {}
+        d->extend({A: 10, Func: function('F', [])})
+      enddef
+
+      Test()
+  END
+  CheckScriptFailure(lines, 'E1001: Variable not found: m')
+enddef
+
 def Test_job_info_return_type()
   if has('job')
     job_start(&shell)