patch 9.1.0515: Vim9: segfault in object_equal()

Problem:  Vim9: segfault in object_equal()
Solution: test for object pointer being NULL, before dereferencing them
          (Ernie Rael)

closes: #15085

Signed-off-by: Ernie Rael <errael@raelity.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/test_vim9_class.vim b/src/testdir/test_vim9_class.vim
index c363cf0..a043f8c 100644
--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -10502,6 +10502,20 @@
     assert_equal(true, result)
   END
   v9.CheckScriptSuccess(lines)
+
+  lines =<< trim END
+    vim9script
+
+    class C
+        public var nest: C
+    endclass
+    var o1 = C.new()
+    var o2 = C.new(C.new())
+
+    var result = o1 == o2
+    assert_equal(false, result)
+  END
+  v9.CheckScriptSuccess(lines)
 enddef
 
 " Test for using a compound operator from a lambda function in an object method